Methods and apparatus for WLAN transmission

ABSTRACT

A modulation coding scheme (MCS) is selected i) from a first set of MCSs when the PHY data unit is to be transmitted using a first channel bandwidth, and ii) from a second set of MCSs when the PHY data unit is to be transmitted using a second channel bandwidth. The first set of MCSs corresponds to i) a number of spatial streams, and ii) the first channel bandwidth, the second set of MCSs corresponds to i) the number of spatial streams, and ii) the second channel bandwidth. The second set of MCSs excludes one or more MCSs in the first set of MCSs that will result in a padding-related constraint not being met when the second channel bandwidth is to be used. Information bits are encoded according to the selected MCS, and modulated according to the selected MCS.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/834,117, entitled “Methods and Apparatus for WLAN Transmission,”filed on Aug. 24, 2015, which is a continuation of U.S. patentapplication Ser. No. 14/221,820, entitled “Methods and Apparatus forWLAN Transmission,” filed on Mar. 21, 2014, which is a divisional ofU.S. patent application Ser. No. 12/846,681, entitled “Method andApparatus for WLAN Transmission,” filed on Jul. 29, 2010, which claimsthe benefit of the following U.S. Provisional patent applications:

U.S. Provisional Patent Application No. 61/229,679, entitled“Transmitter Flow for 80 MHz OFDM,” filed on Jul. 29, 2009;

U.S. Provisional Patent Application No. 61/233,445, entitled“Transmitter Flow for 80 MHz OFDM,” filed on Aug. 12, 2009;

U.S. Provisional Patent Application No. 61/237,215, entitled“Transmitter Flow for 80 MHz OFDM,” filed on Aug. 26, 2009;

U.S. Provisional Patent Application No. 61/266,453, entitled“Transmitter Flow for 80 MHz OFDM,” filed on Dec. 3, 2009;

U.S. Provisional Patent Application No. 61/286,948, entitled“Transmitter Flow for 80/120/160 MHz OFDM,” filed on Dec. 16, 2009;

U.S. Provisional Patent Application No. 61/312,840, entitled“Transmitter Flow for 80/120/160 MHz OFDM,” filed on Mar. 11, 2010; and

U.S. Provisional Patent Application No. 61/316,982, entitled“Transmitter Flow for 80/120/160 MHz OFDM,” filed on Mar. 24, 2010.

The disclosures of all of the patent applications referenced above arehereby incorporated by reference herein in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilizeorthogonal frequency division multiplexing (OFDM).

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Wireless local area network (WLAN) technology has evolved rapidly overthe past decade. Development of WLAN standards such as the Institute forElectrical and Electronics Engineers (IEEE) 802.11a, 802.11b, 802.11g,and 802.11n Standards has improved single-user peak data throughput. Forexample, the IEEE 802.11b Standard specifies a single-user peakthroughput of 11 megabits per second (Mbps), the IEEE 802.11a and802.11g Standards specify a single-user peak throughput of 54 Mbps, andthe IEEE 802.11n Standard specifies a single-user peak throughput of 600Mbps. Work has begun on a new standard, IEEE 802.11ac, that promises toprovide even greater throughput.

SUMMARY

In an embodiment, a method for generating a physical layer (PHY) dataunit for transmission via a communication channel includes selecting, ata communication device, a modulation coding scheme (MCS) i) from a firstset of MCSs when the PHY data unit is to be transmitted using a channelhaving a first channel bandwidth, and ii) from a second set of MCSs whenthe PHY data unit is to be transmitted using a channel having a secondchannel bandwidth. The first set of MCSs corresponds to i) a number ofspatial streams, and ii) the first channel bandwidth, the second set ofMCSs corresponds to i) the number of spatial streams, and ii) the secondchannel bandwidth, the first set of MCSs is different than the secondset of MCSs, and the second set of MCSs excludes one or more MCSs in thefirst set of MCSs that will result in a padding-related constraint notbeing met when the second channel bandwidth is to be used. The methodalso includes: encoding, at the communication device, information bitsusing one or more encoders and according to the selected MCS; parsing,at the communication device, the encoded information bits into thenumber of spatial streams; modulating, at the communication device, theencoded information bits according to the selected MCS; and generating,at the communication device, a plurality of Orthogonal FrequencyDivision Multiplexing (OFDM) symbols based on the modulated encodedinformation bits.

In another embodiment, an apparatus comprises a network interface devicehaving a memory to store indicators of a first set of modulation codingschemes (MCSs) and a second set of MCSs. The first set of MCSscorresponds to i) a number of spatial streams, and ii) the first channelbandwidth, the second set of MCSs corresponds to i) the number ofspatial streams, and ii) the second channel bandwidth, the first set ofMCSs is different than the second set of MCSs, and the second set ofMCSs excludes one or more MCSs in the first set of MCSs that will resultin a padding-related constraint not being met when the second channelbandwidth is to be used. The network interface device is configured toselect an MCS i) from the first set of MCSs when a physical layer (PHY)data unit is to be transmitted using a channel having a first channelbandwidth, and ii) from the second set of MCSs when the PHY data unit isto be transmitted using a channel having a second channel bandwidth. Thenetwork interface device further comprises: one or more encodersconfigured to encode information bits according to the selected MCS; aparser configured to parse the encoded information bits into the numberof spatial streams; and a modulator configured to modulate the encodedinformation bits according to the selected MCS. The network interfacedevice is further configured to generate a plurality of OrthogonalFrequency Division Multiplexing (OFDM) symbols based on the modulatedencoded information bits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment;

FIG. 2 is a block diagram of a prior art physical layer (PHY) unit;

FIG. 3 is a block diagram of a PHY unit, according to an embodiment;

FIGS. 4A-4F are diagrams of various example communication channels viawhich the PHY unit of FIG. 3 is configured to transmit orthogonalfrequency division multiplexing (OFDM) symbols, according to variousembodiments;

FIGS. 5A and 5B are diagrams of two example OFDM symbols for 40 MHzcommunication channels that the PHY unit of FIG. 3 is configured togenerate, according to an embodiment;

FIGS. 6A and 6B are diagrams of two example OFDM symbols for 80 MHzcommunication channels that the PHY unit of FIG. 3 is configured togenerate, according to some embodiments;

FIGS. 7A and 7B are diagrams of two example OFDM symbols for 80 MHzcommunication channels that the PHY unit of FIG. 3 is configured togenerate, according to some embodiments;

FIGS. 8A-8C are diagrams of three example OFDM symbols for 80 MHzcommunication channels, according to some embodiments, where thediagrams show numbers and locations of pilot symbols;

FIGS. 9A and 9B are tables of example pilot symbol values for differentscenarios, according to some embodiments;

FIG. 10 is a block diagram of an example pilot tone system that isimplemented in the PHY unit of FIG. 3, according to some embodiments;

FIG. 11 is a block diagram of an example padding system that isimplemented in the PHY unit of FIG. 3, according to some embodiments;

FIG. 12 is a block diagram of another example padding system that isimplemented in the PHY unit of FIG. 3, according to other embodiments;

FIG. 13 is a block diagram of still another example padding system thatis implemented in the PHY unit of FIG. 3, according to otherembodiments;

FIG. 14 is a diagram of an example aggregated media access control (MAC)layer data unit with MAC layer padding and PHY padding;

FIG. 15 is a table providing some example parameter values for aninterleaver of the PHY unit of FIG. 3, according to one embodiment;

FIG. 16 is a table providing other example parameter values for theinterleaver of the PHY unit of FIG. 3, according to another embodiment;

FIG. 17 is a flow diagram of an example method for generating a OFDMsymbol, according to an embodiment;

FIG. 18 is a flow diagram of an example method for generating OFDMsymbols, according to an embodiment;

FIG. 19 is a flow diagram of another example method for generating OFDMsymbols, according to another embodiment;

FIG. 20 is a flow diagram of another example method for generating OFDMsymbols, according to another embodiment;

FIG. 21 is a flow diagram of another example method for generating OFDMsymbols, according to another embodiment;

FIG. 22 is a flow diagram of another example method for generating OFDMsymbols, according to another embodiment; and

FIG. 23 is a flow diagram of another example method for generating OFDMsymbols, according to another embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. The AP is configured to operatewith client stations according to at least a first communicationprotocol. In one embodiment, the first communication protocol is theIEEE 802.11ac Standard, now in the process of being standardized. Inother embodiments, the first communication protocol is a protocol otherthan the IEEE 802.11ac Standard. In some embodiments or scenarios, oneor more client stations in the vicinity of the AP are not configured tooperate according to the first communication protocol, but areconfigured to operate according to at least a second communicationprotocol. Therefore, in some embodiments, the AP is additionallyconfigured to operate with client stations according to at least asecond communication protocol.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) unit 18 and a physical layer(PHY) unit 20. The PHY unit 20 includes a plurality of transceivers 21,and the transceivers are coupled to a plurality of antennas 24. Althoughthree transceivers 21 and three antennas 24 are illustrated in FIG. 1,the AP 14 can include different numbers (e.g., 1, 2, 4, 5, etc.) oftransceivers 21 and antennas 24 in other embodiments. In one embodiment,the MAC unit 18 and the PHY unit 20 are configured to operate accordingto a first communication protocol (e.g., the IEEE 802.11ac Standard, nowin the process of being standardized). In another embodiment, the MACunit 18 and the PHY unit 20 are also configured to operate according toat least a second communication protocol (e.g., the IEEE 802.11nStandard, the IEEE 802.11a Standard, etc.).

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 can includedifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. At least one of the client stations25 (e.g., client station 25-1) is configured to operate at leastaccording to the first communication protocol. In some embodiments, atleast one of the client stations 25 is not configured to operateaccording to the first communication protocol but is configured tooperate according to at least the second communication protocol(referred to herein as a “legacy client station”).

The client station 25-1 includes a host processor 26 coupled to anetwork interface 27. The network interface 27 includes a MAC unit 28and a PHY unit 29. The PHY unit 29 includes a plurality of transceivers30, and the transceivers 30 are coupled to a plurality of antennas 34.Although three transceivers 30 and three antennas 34 are illustrated inFIG. 1, the client station 25-1 can include different numbers (e.g., 1,2, 4, 5, etc.) of transceivers 30 and antennas 34 in other embodiments.

In an embodiment, one or both of the client stations 25-2 and 25-3, hasa structure the same as or similar to the client station 25-1. In anembodiment, the client station 25-4, has a structure similar to theclient station 25-1. In these embodiments, the client stations 25structured the same as or similar to the client station 25-1 have thesame or a different number of transceivers and antennas. For example,the client station 25-2 has only two transceivers and two antennas,according to an embodiment.

According to an embodiment, the client station 25-4 is a legacy clientstation, i.e., the client station 25-4 is not enabled to receive andfully decode a data unit that is transmitted by the AP 14 or anotherclient station 25 according to the first communication protocol.Similarly, according to an embodiment, the legacy client station 25-4 isnot enabled to transmit data units according to the first communicationprotocol. On the other hand, the legacy client station 25-4 is enabledto receive and fully decode and transmit data units according to thesecond communication protocol.

In various embodiments, the PHY unit 20 of the AP 14 is configured togenerate data units conforming to the first communication protocol. Thetransceiver(s) 21 is/are configured to transmit the generated data unitsvia the antenna(s) 24. Similarly, the transceiver(s) 24 is/areconfigured to receive the data units via the antenna(s) 24. The PHY unit20 of the AP 14 is configured to process received data units conformingto the first communication protocol, according to an embodiment.

In various embodiments, the PHY unit 29 of the client device 25-1 isconfigured to generate data units conforming to the first communicationprotocol. The transceiver(s) 30 is/are configured to transmit thegenerated data units via the antenna(s) 34. Similarly, thetransceiver(s) 30 is/are configured to receive data units via theantenna(s) 34. The PHY unit 29 of the client device 25-1 is configuredto process received data units conforming to the first communicationprotocol, according to an embodiment.

FIG. 2 is a block diagram of a prior art PHY unit 100 configured tooperate according to the IEEE 802.11n Standard. The PHY unit 100 isincluded in the legacy client 25-4 (FIG. 1), in one embodiment. The PHYunit 100 includes a scrambler 104 that generally scrambles aninformation bit stream to reduce the occurrence of long sequences ofones or zeros and to generate a scrambled stream. An encoder parser 108demultiplexes the scrambled stream into one or two encoder input streamscorresponding to one or two forward error correction (FEC) encoders 112.Each encoder 112 encodes the corresponding input stream to generate acorresponding encoded stream.

A stream parser 116 parses the one or two encoded streams into up tofour spatial streams. Corresponding to each spatial stream, aninterleaver 120 interleaves bits of the spatial stream (i.e., changesthe order of the bits) to prevent long sequences of adjacent noisy bitsfrom entering a decoder at the receiver. Also corresponding to eachspatial stream, a constellation mapper 124 maps an interleaved sequenceof bits to constellation points corresponding to different subcarriersof an orthogonal frequency division multiplexing (OFDM) symbol.

A space-time block coding unit 128 receives the constellation pointscorresponding to the one or more spatial streams and spreads the spatialstreams to a greater number of space-time streams. The space-time blockcoding unit 128 can be controlled to merely pass through spatial streamswithout performing space-time block coding. For example, when the numberof spatial streams is four, the space-time block coding unit 128 doesnot perform space-time block coding.

A plurality of cyclic shift diversity (CSD) units 132 insert cyclicshifts into all but one of the space-time streams (if more than onespace-time stream). The cyclic shifts are to prevent unintentionalbeamforming.

A spatial mapping unit 136 maps the space-time streams to transmitchains. Spatial mapping may include: 1) direct mapping, in whichconstellation points from each space-time stream are mapped directlyonto transmit chains (i.e., one-to-one mapping); 2) spatial expansion,in which vectors of constellation point from all space-time streams areexpanded via matrix multiplication to produce inputs to the transmitchains; and 3) beamforming, in which each vector of constellation pointsfrom all of the space-time streams is multiplied by a matrix of steeringvectors to produce inputs to the transmit chains.

Each output of the spatial mapping unit 136 corresponds to a transmitchain, and each output of the spatial mapping unit 136 is operated on byan inverse discrete Fourier transform (IDFT) unit 140 that converts ablock of constellation points to a time-domain signal.

Outputs of the IDFT units 140 are provided to guard interval (GI)insertion and windowing units 144 that prepends, to an OFDM symbol, acircular extension of the OFDM symbol and smooths the edges of eachsymbol to increase spectral decay. Outputs of the GI insertion andwindowing units 144 are provided to analog and radio frequency (RF)units that convert the signals to analog signals and upconvert thesignals to RF frequencies for transmission. The IEEE 802.11n Standardspecifies that signals are transmitted in either a 20 MHz bandwidthchannel or a 40 MHz bandwidth channel.

Referring again to FIG. 1, the AP 14 and the clients 25-1, 25-2, 25-3are configured to transmit and receive signals that conform to the firstcommunication protocol. In some embodiments, the first communicationprotocol permits transmission in a channel having a bandwidth of atleast 80 MHz. For instance, in some embodiments, the first communicationprotocol permits transmission in a channel having a bandwidth of 80 MHz,120 MHz, 160 MHz, etc. In some embodiments, the first communicationprotocol permits transmission with different bandwidths such as two ormore of 80 MHz, 120 MHz, 160 MHz, etc.

Additionally, in some embodiments, the first communication protocol isgenerally backwards compatible with older communication protocols, suchas one or both of the IEEE 802.11a Standard and the IEEE 802.11nStandard. For example, in one embodiment, the first communicationprotocol specifies a PHY data unit format such as one or more of theformats in U.S. patent application Ser. No. 12/758,603, filed on Apr.12, 2010, and entitled “Physical Layer Frame Format”, which is herebyincorporated by reference herein, in its entirety.

FIG. 3 is a block diagram of an example PHY unit 200 configured tooperate according to the first communication protocol, according to anembodiment. Referring to FIG. 1, the AP 14 and the client station 25-1,in one embodiment, each include a PHY unit such as the PHY unit 200.

The PHY unit 200 includes a scrambler 204 that generally scrambles aninformation bit stream to reduce the occurrence of long sequences ofones or zeros. The IEEE 802.11a Standard and the 802.11n Standardspecify a 127-length scrambler with a generator polynomial S(x) givenby:S(x)=x ⁷ +x ⁴+1  Equ. 1The polynomial S(x) is also utilized for descrambling an information bitstream at the receiver. In one embodiment, the scrambler 204 implementsa 127-length scrambler with a generator polynomial S(x) given by Equ. 1.Also in this embodiment, a receiver configured to operate according tothe first communication protocol also utilizes the generator polynomialS(x) given by Equ. 1. In other embodiments, the scrambler 204 implementsa length different than 127 and/or utilizes a generator polynomialdifferent than the generator polynomial S(x) given by Equ. 1. In anotherembodiment, the scrambler 204 is replaced with a plurality of parallelscramblers located after an encoder parser 208. In this embodiment, eachof the parallel scramblers has a respective output coupled to arespective one of a plurality of FEC encoders 212. The plurality ofparallel scramblers operate simultaneously on a demultiplexed stream. Inanother embodiment, the scrambler 204 comprises a plurality of parallelscramblers and a demultiplexer that demultiplexes the information bitstream to the plurality of parallel scramblers, which operatesimultaneously on demultiplexed streams. These embodiments may beuseful, in some scenarios, to accommodate wider bandwidths and thushigher operating clock frequencies.

The encoder parser 208 is coupled to the scrambler 204. The encoderparser 208 demultiplexes the information bit stream into one or moreencoder input streams corresponding to one or more FEC encoders 212. Inanother embodiment with a plurality of parallel scramblers, the encoderparser 208 demultiplexes the information bit stream into a plurality ofstreams corresponding to the plurality of parallel scramblers.

Each encoder 212 encodes the corresponding input stream to generate acorresponding encoded stream. In one embodiment, each FEC encoder 212includes a binary convolutional encoder. In another embodiment, each FEC212 encoder includes a binary convolutional encoder followed by apuncturing block. In another embodiment, each FEC encoder 212 includes alow density parity check (LDPC) encoder. In another embodiment, each FECencoder 212 includes a binary convolutional encoder followed by apuncturing block. In yet another embodiment, each FEC encoder 212additionally includes an LDPC encoder. In this embodiment, each FECencoder 212 is configured to implement any of: 1) binary convolutionalencoding without puncturing; 2) binary convolutional encoding withpuncturing; or 3) LDPC encoding.

Different numbers of encoders 212 may operate in parallel depending onthe data rate of a particular modulation coding scheme (MCS). In oneembodiment, the PHY unit 200 includes five encoders 212, and one, two,three, four, or five encoders operate simultaneously depending on theparticular MCS being utilized. In another embodiment, the PHY unit 200includes four encoders 212, and one, two, three, or four encodersoperate simultaneously depending on the particular MCS being utilized.In another embodiment, the PHY unit 200 includes four encoders 212, andone, two, or four encoders operate simultaneously depending on theparticular MCS being utilized. In another embodiment, the PHY unit 200includes three encoders 212, and one, two, or three encoders operatesimultaneously depending on the particular MCS being utilized. Inanother embodiment, the PHY unit 200 includes up to eight encoders 212,and one, two, three, four, five, six, seven, or eight encoders operatesimultaneously depending on the particular MCS being utilized. Inanother embodiment, the PHY unit 200 includes up to eight encoders 212,and one, two, three, four, six, or eight encoders operate simultaneouslydepending on the particular MCS being utilized. In another embodiment,the PHY unit 200 includes up to eight encoders 212, and one, two, four,six, or eight encoders operate simultaneously depending on theparticular MCS being utilized.

In one embodiment, the number of encoders utilized increments according450 Mbps step sizes in the data rate. In other embodiments, the numberof encoders utilized increments according to a step size in the datarate that is between approximately 400 and 500 Mbps. In anotherembodiment, the number of encoders utilized increments according to astep size in the data rate that is between approximately 400 and 600Mbps. In one embodiment, the step size is 600 Mbps.

A stream parser 216 parses the one or more encoded streams into one ormore spatial streams for separate interleaving and mapping intoconstellation points. In one embodiment, the stream parser 216 uses theoutput of each operating encoder 212 in a round robin fashion, using Sbits from each operating encoder per cycle, where:

$\begin{matrix}{{S = {\sum\limits_{i = 1}^{N_{ss}}{\max\left\{ {1,\frac{N_{BPSCS}\left( i_{ss} \right)}{2}} \right\}}}},} & {{Equ}.\mspace{14mu} 2}\end{matrix}$and where N_(SS) is the number of spatial streams and N_(BPSCS)(i_(SS))is the number of coded bits per carrier for spatial stream i_(SS).

Corresponding to each spatial stream, an interleaver 220 interleavesbits of the spatial stream (i.e., changes the order of the bits) toprevent long sequences of adjacent noisy bits from entering a decoder atthe receiver. Compared to the interleavers 120 (FIG. 2) of the IEEE802.11n Standard compliant PHY unit 100, the interleavers 220 areextended to cover longer bit streams corresponding to wider bandwidthOFDM symbols, such as 80 MHz, 120 MHz, 160 MHz, etc. As will bedescribed further below, in some embodiments of the PHY unit 200, atransmit chain includes multiple radios so that a wideband OFDM symbolis transmitted as multiple sub-OFDM symbols via respective radios. Forexample, an 80 MHz-wide OFDM symbol is transmitted via two radios, eachhaving a bandwidth of 40 MHz. As another example, a 160 MHz-wide OFDMsymbol is transmitted via two radios, each having a bandwidth of 80 MHz.As another example, a 160 MHz-wide OFDM symbol is transmitted via fourradios, each having a bandwidth of 40 MHz. In one embodiment in which awide-band OFDM symbol is transmitted via multiple radios, multipleinterleavers 220 may be utilized such that a separate interleaver 220corresponds to each radio used to transmit the wide-band OFDM symbol.

Also corresponding to each spatial stream, a constellation mapper 224maps an interleaved sequence of bits to constellation pointscorresponding to different subcarriers of an OFDM symbol. Morespecifically, for each spatial stream, the constellation mapper 224translates every bit sequence of length log₂(M) into one of Mconstellation points. The constellation mapper 224 handles differentnumbers of constellation points depending on the MCS being utilized. Inan embodiment, the constellation mapper 224 is a quadrature amplitudemodulation (QAM) mapper that handles M=2, 4, 16, 64, 256, and 1024. Inother embodiments, the constellation mapper 224 handles differentmodulation schemes corresponding to M equaling different subsets of atleast two values from the set {2, 4, 16, 64, 256, 1024}.

A space-time block coding unit 228 receives the constellation pointscorresponding to the one or more spatial streams and spreads the spatialstreams to a greater number of space-time streams. The space-time blockcoding unit 228 can be controlled to merely pass through spatial streamswithout performing space-time block coding. For example, when the numberof spatial streams is equal to the maximum number of space-time streams,the space-time block coding unit 228 does not perform space-time blockcoding. In some embodiments, the space-time block coding unit 228 isomitted.

A plurality of CSD units 232 insert cyclic shifts into all but one ofthe space-time streams (if more than one space-time stream). The cyclicshifts are to prevent unintentional beamforming. For ease ofexplanation, the inputs to the CSD units 232 are referred to asspace-time streams even in embodiments in which the space-time blockcoding unit 228 is omitted. In one embodiment, the frequency CDD valuesapplied on each of four space-time streams is the same as the frequencyCDD values specified in the IEEE 802.11n Standard. In anotherembodiment, the frequency CDD values applied on each of four space-timestreams is different than the frequency CDD values specified in the IEEE802.11n Standard. In one embodiment, if more than four space-timestreams are utilized, the frequency CDD values are defined similarly tothe definitions in the IEEE 802.11n Standard.

In one embodiment, the time CDD values applied on each of fourspace-time streams is the same as the time CDD values specified in theIEEE 802.11n Standard. In another embodiment, the time CDD valuesapplied on each of four space-time streams is different than the timeCDD values specified in the IEEE 802.11n Standard. In one embodiment, ifmore than four space-time streams are utilized, the time CDD values aredefined to be values within the range [−200 0] ns. In anotherembodiment, if more than four space-time streams are utilized, the timeCDD values are defined to be values within a suitable range differentthan the range [−200 0] ns.

A spatial mapping unit 236 maps the space-time streams to transmitchains. In various embodiments, spatial mapping includes one or moreof: 1) direct mapping, in which constellation points from eachspace-time stream are mapped directly onto transmit chains (i.e.,one-to-one mapping); 2) spatial expansion, in which vectors ofconstellation point from all space-time streams are expanded via matrixmultiplication to produce inputs to the transmit chains; and 3)beamforming, in which each vector of constellation points from all ofthe space-time streams is multiplied by a matrix of steering vectors toproduce inputs to the transmit chains.

In one embodiment, the spatial mapping unit 236 applies a steeringmatrix Q (e.g., multiplies an N_(STS)×1 signal vector s by Q, i.e., Qs),where Q has a size (N_(TX)×N_(STS)), where N_(TX) is the number oftransmit chains and N_(STS) is the number of space-time streams. Whenbeamforming is utilized, the matrix Q is generated based on the MIMOchannel between the transmitter and the receiver. In one embodiment,N_(TX) has a maximum value of 8. In another embodiment, N_(TX) has amaximum value of 16. In other embodiments, N_(TX) has a differentmaximum value such as 4, 32, 64, etc.

Each output of the spatial mapping unit 236 corresponds to a transmitchain, and each output of the spatial mapping unit 236 is operated on byan IDFT unit 240 that converts a block of constellation points to atime-domain signal.

Outputs of the IDFT units 240 are provided to GI insertion and windowingunits 244 that prepend, to each OFDM symbol, a circular extension of theOFDM symbol and smooth the edges of each symbol to increase spectraldecay. Outputs of the GI insertion and windowing units 244 are providedto analog and RF units 248 that convert the signals to analog signalsand upconvert the signals to RF frequencies for transmission. As will bediscussed below, the signals are transmitted in a 20 MHz, a 40 MHz, an80 MHz, a 120 MHz, or a 160 MHz bandwidth channel, in variousembodiments and/or scenarios.

Example communication channel characteristics and OFDM subcarrierconfigurations that correspond to transmit signals generated by theexample PHY unit 200 of FIG. 3, according to several embodiments, willnow be discussed.

Channels

FIGS. 4A-4F are diagrams of communication channels via which signals aretransmitted according to the first communication protocol, in someembodiments. The PHY unit 200 (FIG. 3) is configured, in someembodiments, to generate transmit signals that occupy a channel such asone of the channels of FIGS. 4A-4F, or another suitable channel. In someembodiments, PHY unit 200 (FIG. 3) is configured to generate transmitsignals corresponding to different channels, such as the channels ofFIGS. 4A-4F, or other suitable channels, depending on channelconditions, the capabilities of the receive device, etc.

FIG. 4A is a diagram showing an example contiguous 80 MHz channel 270.In one embodiment, the channel 270 is transmitted using a single radiotransceiver architecture. In another embodiment, the channel 270 istransmitted using a dual radio transceiver architecture having twoseparate front end blocks. For example, in this embodiment, a firstradio transceiver transmits a lower portion of the channel 270, and asecond radio transceiver transmits an upper portion of the channel 270.Referring again to FIG. 3, in one embodiment, separate IDFT blocks 240,separate GI insertion and windowing units 244, and separate analog andRF units 248 generate the lower and upper portions, whereas scrambling,encoding, interleaving, constellation mapping, etc., operate over theentire 80 MHz channel. In another embodiment, separate scrambling units204, separate encoders 212, separate interleaving units 220, separateconstellation mapping units 224, etc, and separate IDFT blocks 240,separate GI insertion and windowing units 244, and separate analog andRF units 248 generate the lower and upper portions.

FIG. 4B is a diagram showing an example contiguous 120 MHz channel 274.In one embodiment, the channel 274 is transmitted using a single radiotransceiver architecture. In another embodiment, the channel 274 istransmitted using a dual radio transceiver architecture having twoseparate front end blocks. For example, in this embodiment, a firstradio transceiver transmits a lower portion of the channel 274, and asecond radio transceiver transmits an upper portion of the channel 274.In one embodiment, one of the upper portion and the lower portion has abandwidth of 80 MHz, and the other of the upper portion and the lowerportion has a bandwidth of 40 MHz. Referring again to FIG. 3, in oneembodiment, separate IDFT blocks 240, separate GI insertion andwindowing units 244, and separate analog and RF units 248 generate thelower and upper portions, whereas scrambling, encoding, interleaving,constellation mapping, etc., operate over the entire 120 MHz channel. Inanother embodiment, separate scrambling units 204, separate encoders212, separate interleaving units 220, separate constellation mappingunits 224, etc, and separate IDFT blocks 240, separate GI insertion andwindowing units 244, and separate analog and RF units 248 generate thelower and upper portions.

FIG. 4C is a diagram showing an example contiguous 160 MHz channel 278.In one embodiment, the channel 278 is transmitted using a single radiotransceiver architecture. In another embodiment, the channel 278 istransmitted using a dual radio transceiver architecture having twoseparate front end blocks. For example, in this embodiment, a firstradio transceiver transmits a lower portion of the channel 278, and asecond radio transceiver transmits an upper portion of the channel 278.Referring again to FIG. 3, in one embodiment, separate IDFT blocks 240,separate GI insertion and windowing units 244, and separate analog andRF units 248 generate the lower and upper portions, whereas scrambling,encoding, interleaving, constellation mapping, etc., operate over theentire 160 MHz channel. In another embodiment, separate scrambling units204, separate encoders 212, separate interleaving units 220, separateconstellation mapping units 224, etc, and separate IDFT blocks 240,separate GI insertion and windowing units 244, and separate analog andRF units 248 generate the lower and upper portions.

FIG. 4D is a diagram showing an example non-contiguous 80 MHz channel282, having a lower portion and an upper portion separated in frequencyby some minimum bandwidth such as 1 MHz, 5 MHz, 10 MHz, 20 MHz, 40 MHz,etc., or some other suitable minimum bandwidth. In other words, theupper and lower portions are disjoint. In another embodiment, there isnot a minimum separation, and the distance (in frequency) between theupper and lower portions is permitted to reach as little as zero, insome scenarios. In one embodiment, the channel 282 is transmitted usinga dual radio transceiver architecture having two separate front endblocks. For example, in this embodiment, a first radio transceivertransmits a lower portion of the channel 282, and a second radiotransceiver transmits an upper portion of the channel 282. In oneembodiment having a dual radio transceiver architecture, the PHY unit isconfigured to additionally generate a contiguous channel with the dualradios. In this embodiment, the lower portion and the upper portion areconsidered to be separated in frequency by 0 MHz, i.e., the lowerportion and the upper portion are not separated in frequency and arethus contiguous. Referring again to FIG. 3, in one embodiment, separateIDFT blocks 240, separate GI insertion and windowing units 244, andseparate analog and RF units 248 generate the lower and upper portions,whereas scrambling, encoding, interleaving, constellation mapping, etc.,operate over the entire 80 MHz channel. In another embodiment, separatescrambling units 204, separate encoders 212, separate interleaving units220, separate constellation mapping units 224, etc, and separate IDFTblocks 240, separate GI insertion and windowing units 244, and separateanalog and RF units 248 generate the lower and upper portions.

FIG. 4E is a diagram showing an example non-contiguous 120 MHz channel286, having a lower portion and an upper portion separated in frequencyby some suitable minimum bandwidth. In one embodiment, the channel 286is transmitted using a dual radio transceiver architecture having twoseparate front end blocks. For example, in this embodiment, a firstradio transceiver transmits a lower portion of the channel 286, and asecond radio transceiver transmits an upper portion of the channel 286.Referring again to FIG. 3, in one embodiment, separate IDFT blocks 240,separate GI insertion and windowing units 244, and separate analog andRF units 248 generate the lower and upper portions, whereas scrambling,encoding, interleaving, constellation mapping, etc., operate over theentire 120 MHz channel. In another embodiment, separate scrambling units204, separate encoders 212, separate interleaving units 220, separateconstellation mapping units 224, etc, and separate IDFT blocks 240,separate GI insertion and windowing units 244, and separate analog andRF units 248 generate the lower and upper portions.

FIG. 4F is a diagram showing an example non-contiguous 160 MHz channel290, having a lower portion and an upper portion separated in frequencyby some suitable minimum bandwidth. In one embodiment, the channel 290is transmitted using a dual radio transceiver architecture having twoseparate front end blocks. For example, in this embodiment, a firstradio transceiver transmits a lower portion of the channel 290, and asecond radio transceiver transmits an upper portion of the channel 290.Referring again to FIG. 3, in one embodiment, separate IDFT blocks 240,separate GI insertion and windowing units 244, and separate analog andRF units 248 generate the lower and upper portions, whereas scrambling,encoding, interleaving, constellation mapping, etc., operate over theentire 160 MHz channel. In another embodiment, separate scrambling units204, separate encoders 212, separate interleaving units 220, separateconstellation mapping units 224, etc, and separate IDFT blocks 240,separate GI insertion and windowing units 244, and separate analog andRF units 248 generate the lower and upper portions.

Similarly, in some embodiments, contiguous 10 MHz and 20 MHz channelsare transmitted using a single radio transceiver architecture. In otherembodiments, contiguous or non-contiguous 10 MHz and 20 MHz channels aretransmitted in upper portions and lower portions in a manner similar tothat discussed with respect to FIGS. 4A-4E. More generally, thebandwidth of the channel is any suitable bandwidth, and is not limitedto 10 MHz, 20 MHz, 40 MHz, 80 MHz, 120 MHz, and 160 MHz. Additionally, achannel may be transmitted in three or more non-contiguous portionsusing a multiple radio transceiver architecture having three or moreseparate front end blocks.

In some embodiments, the portions (e.g., upper and lower) of acontiguous or non-contiguous channel are the same bandwidth, such asillustrated in FIGS. 4A-4D and 4F. On the other hand, in someembodiments, the portions (e.g., upper and lower) of a channel havedifferent bandwidths, as illustrated in FIG. 4E.

IDFT/DFT Structure

According to the IEEE 802.11a Standard, an OFDM signal for a 20 MHzchannel is generated using a size 64 IDFT. Similarly, according to theIEEE 802.11n Standard, an OFDM signal for a 20 MHz channel is generatedusing a size 64 IDFT, and an OFDM signal for a 40 MHz channel isgenerated using a size 128 IDFT.

The PHY unit 200 (FIG. 3) is configured, in some embodiments, togenerate OFDM symbols for transmission via channels, such as discussedabove.

In one embodiment, an OFDM signal for an 80 MHz channel is generatedusing a size 256 IDFT, and an OFDM signal for a 160 MHz channel isgenerated using a size 512 IDFT. In another embodiment, an OFDM signalfor a 160 MHz channel is generated using a size 256 IDFT, correspondingto a lower 80 MHz portion, and a size 256 IDFT, corresponding to anupper 80 MHz portion. In one embodiment, an OFDM signal for a 120 MHzchannel is generated using a size 128 IDFT, corresponding to a 40 MHzportion, and a size 256 IDFT, corresponding to an 80 MHz portion. ThePHY unit 200 (FIG. 3) is configured, in some embodiments, to generateIDFTs of different suitable sizes such as one or more of a size 64 IDFT,a size 128 IDFT, a size 256 IDFT, a size 512 IDFT, etc. Referring toFIG. 3, for example, each of the IDFT units 240 is configured togenerate IDFTs of different suitable sizes such as one or more of a size64 IDFT, a size 128 IDFT, a size 256 IDFT, a size 512 IDFT, etc.

Tone Mapping/Subcarrier Design

FIGS. 5A, 5B, 6A, 6B, 7A, and 7B are diagrams of OFDM symbols that aregenerated according to the first communication protocol, in someembodiments. The PHY unit 200 (FIG. 3) is configured, in someembodiments, to generate OFDM symbols such as one of the OFDM symbols ofFIGS. 5A, 5B, 6A, 6B, 7A, and 7B, or another suitable OFDM symbol. Insome embodiments, PHY unit 200 (FIG. 3) is configured to generatedifferent OFDM symbols, such as the OFDM symbols of FIGS. 5A, 5B, 6A,6B, 7A, and 7B, or other suitable OFDM symbols, depending on channelconditions, the capabilities of the receive device to which the OFDMsymbol is being transmitted, etc.

Referring now to FIG. 5A, an OFDM symbol 310 for a 20 MHz channel,according to one embodiment, corresponds to a size 64 IDFT and includes64 tones. The 64 tones are indexed from −32 to +31, in an embodiment.The 64 tones include 11 guard tones, a direct current (DC) tone, datatones, and pilot tones. The four lowest frequency tones and the threehighest frequency tones are guard tones, which are provided for filterramp up and ramp down. The index-0 tone is a DC tone, which is providedfor mitigating radio frequency interference. The OFDM symbol 310includes 56 data/pilot tones. The OFDM symbol 310 has the same format asspecified in the IEEE 802.11n Standard.

Referring now to FIG. 5B, an OFDM symbol 330 for a 40 MHz channel,according to one embodiment, corresponds to a size 128 IDFT and includes128 tones. The 128 tones are indexed from −64 to +63, in an embodiment.The 128 tones include guard tones, DC tones, data tones, and pilottones. The six lowest frequency tones and the five highest frequencytones are guard tones. The three tones indexed from −1 to +1 are DCtones. The OFDM symbol 330 includes 114 data/pilot tones. The OFDMsymbol 330 has the same format as specified in the IEEE 802.11nStandard.

Referring now to FIG. 6A, an OFDM symbol 350 for an 80 MHz channel,according to one embodiment, corresponds to a size 256 IDFT (or two 128IDFTs) and includes 256 tones. The 256 tones are indexed from −128 to+127, in an embodiment. The 256 tones include guard tones, DC tones,data tones, and pilot tones. The six lowest frequency tones and the fivehighest frequency tones are guard tones. The three tones indexed from −1to +1 are DC tones. The OFDM symbol 350 includes 242 data/pilot tones.

Referring now to FIG. 6B, an OFDM symbol 370 for an 80 MHz channel,according to one embodiment, corresponds to a size 256 IDFT (or two 128IDFTs) and includes 256 tones. The 256 tones are indexed from −128 to+127, in an embodiment. The 256 tones include guard tones, DC tones,data tones, and pilot tones. The four lowest frequency tones and thethree highest frequency tones are guard tones. The three tones indexedfrom −1 to +1 are DC tones. The OFDM symbol 370 includes 246 data/pilottones.

In some embodiments, an OFDM symbol for an 80 MHz channel corresponds totwo concatenated 40 MHz OFDM symbols. For example, referring now to FIG.7A, an OFDM symbol 390 for an 80 MHz channel, according to anotherembodiment, corresponds to a size 256 IDFT (or two 128 IDFTs) andincludes 256 tones. The 256 tones are indexed from −128 to +127, in anembodiment. The 256 tones include guard tones, null tones, DC tones,data tones, and pilot tones. The six lowest frequency tones and the fivehighest frequency tones are guard tones. Eleven tones indexed from −5 to+5 are DC tones. Three tones indexed from −63 to −65 and three tonesindexed from +63 to +65 are null tones. The OFDM symbol 390 includes 57data/pilot tones indexed from −6 to −62, 57 data/pilot tones indexedfrom −66 to −122, 57 data/pilot tones indexed from +6 to +62, and 57data/pilot tones indexed from +66 to +122. Comparing FIG. 7A, with FIG.5B, the 80 MHz OFDM symbol 390 corresponds to two concatenated 40 MHzOFDM symbols 330.

Referring now to FIG. 7B, an OFDM symbol 410 for a non-contiguous 80 MHzchannel, according to one embodiment, corresponds to a size 256 IDFT (ortwo 128 IDFTs), includes 256 tones with a separation in frequencybetween an lower 40 MHz sideband and an upper 40 MHz sideband. ComparingFIG. 7B, with FIG. 5B, the 80 MHz OFDM symbol 390 corresponds to two 40MHz OFDM symbols 330, with a frequency separation between the two OFDMsymbols 330.

With OFDM symbols for 120 MHz and 160 MHz communication channels, amultiple radio PHY unit is utilized, in some embodiments. In someembodiments, 120 MHz and 160 MHz OFDM symbols are formed byconcatenating two or more 40 MHz and/or 80 MHz OFDM symbols, in a mannersimilar to the example OFDM symbols of FIGS. 7A and 7B. In someembodiments utilizing multiple radio PHY units, concatenated OFDMsymbols are separated in frequency, such as in FIG. 7B, in somescenarios.

Pilot Tones

Communication systems that utilize OFDM modulation often utilize pilottones for frequency offset estimation, for example, and some tones orsub-carriers are reserved for pilots. For instance, the IEEE 802.11nStandard specifies that 20 MHz OFDM symbols have four pilot tones atsub-carrier indices {±7, ±21}. Similarly, the IEEE 802.11n Standardspecifies that 40 MHz OFDM symbols have six pilot tones at sub-carrierindices {±11, ±25, ±53}.

In an embodiment of the first communication protocol that is backwardcompatible with the IEEE 802.11n Standard, at least some of the pilotpositions are kept the same as specified in the IEEE 802.11n Standard.

FIG. 8A is a diagram of the OFDM symbol 350 (FIG. 6A) for an 80 MHzchannel and showing example locations of pilot tones, according to oneembodiment. The OFDM symbol 350 includes ten pilot tones at sub-carrierindices {±11, ±39, ±75, ±89, ±117}, in one embodiment. FIG. 8B is adiagram of the OFDM symbol 370 (FIG. 6B) for an 80 MHz channel andshowing example locations of pilot tones, according to one embodiment.The OFDM symbol 350 includes twelve pilot tones at sub-carrier indices{±11, ±39, ±53, ±75, ±89, ±117}, in one embodiment. FIG. 8C is a diagramof the OFDM symbol 350 (FIG. 6A) for an 80 MHz channel and showingexample locations of pilot tones, according to another embodiment. TheOFDM symbol 350 includes eight pilot tones at sub-carrier indices {±11,±39, ±75, ±103}, in one embodiment.

More generally, in some embodiments, an 80 MHz OFDM symbol has one of i)eight, ii) ten, or iii) twelve pilot tones at location pairs belongingto the set of {±11, ±25, ±39, ±53, ±75, ±89, ±103, ±117}. In otherembodiments, different numbers of pilot tones and/or different locationpairs than discussed above are utilized. For 120 MHz and 160 MHz OFDMsymbols, numbers of pilot tones and pilot tone locations are chosenbased on positions of pilots in constituent 40 MHz and/or 80 MHz OFDMsymbols, in some embodiments. In other embodiments, numbers of pilottones and pilot tone locations for 120 MHz and 160 MHz OFDM symbols arechosen irregardless of the positions of pilots in 40 MHz and/or 80 MHzOFDM symbols utilized in the first communication protocol.

In the IEEE 802.11n Standard, pilot values for L pilots (L=4 for a 20MHz OFDM symbol, and L=6 for a 40 MHz OFDM symbol) on the n-th pilotsymbol on the i-th spatial stream are given by:P _(i,n)=└Ψ_(i,n % L)Ψ_(i,(n+1)% L) . . . Ψ_(i,(n+L−1)%)┘,  Equ. 3where P_(i,n) is a vector of L pilot values for the n-th OFDM symbol ofthe i-th spatial stream, and Ψ_(i,j) are pilot values. For the IEEE802.11n Standard, each Ψ_(i,j) belongs to the set of {−1, 1}.

In one embodiment, pilot tone values for 80 MHz OFDM symbols are chosensimilarly to pilot values in 20 MHz and 40 MHz OFDM symbols. FIG. 9A isa table showing example pilot values for 80 MHz OFDM symbols havingeight pilots, for up to four spatial streams. In FIG. 9A, N_(STS) is thenumber of space-time streams (sometimes referred to herein as spatialstreams), and i_(STS) is a space-time stream index. FIG. 9B is a tableshowing example pilot values for 80 MHz OFDM symbols having ten pilots,for up to four spatial streams.

In other embodiment, the columns of the examples tables of FIGS. 9A and9B are permuted to yield new pilot tone value patterns.

In one embodiment, pilot tone values with eight pilots for exactly eightspatial (or space-time) streams is:

$\begin{matrix}{\begin{bmatrix}1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 \\1 & 1 & 1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} \\1 & {- 1} & 1 & {- 1} & {- 1} & 1 & {- 1} & 1 \\1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} & 1 & 1 \\1 & {- 1} & {- 1} & 1 & {- 1} & 1 & 1 & {- 1}\end{bmatrix},} & {{Equ}.\mspace{14mu} 4}\end{matrix}$where the rows correspond to spatial streams and the columns correspondto pilots. The matrix of Equ. 4 is a Hadamard matrix. For fewer thaneight spatial streams, the first N_(SS) rows of the matrix of Equ. 4 arechosen, in an embodiment.

In one embodiment, pilot values for 120 MHz and 160 MHz OFDM symbols arechosen to be a combination of pilot value patterns specified in the IEEE802.11n Standard for 40 MHz OFDM symbols, and/or pilot value patternsfor 80 MHz OFDM symbols.

Data Tones

With the example tone mappings for 80 MHz OFDM symbols discussed abovewith reference to FIGS. 6A, 6B, 7A, and 7B, and with different numbersof pilot tones, the number of sub-carriers that remain for datatransmission can be determined. For example, with OFDM symbol 370 ofFIG. 6B, there are 238 data tones when eight pilot tones are utilized,236 data tones when ten pilot tones are utilized, and 234 data toneswhen twelve pilot tones are utilized. As another example, with OFDMsymbol 350 of FIG. 6A, there are 234 data tones when eight pilot tonesare utilized, 232 data tones when ten pilot tones are utilized, and 230data tones when twelve pilot tones are utilized. As yet another example,with OFDM symbol 390 of FIG. 7A or the OFDM symbol 410 of FIG. 7B, thereare 220 data tones when eight pilot tones are utilized, 218 data toneswhen ten pilot tones are utilized, and 216 data tones when twelve pilottones are utilized. In one embodiment, with OFDM symbol 390 of FIG. 7Aor the OFDM symbol 410 of FIG. 7B, only twelve pilot tones are utilizedthus providing 216 data tones. More generally, depending on theparticular OFDM symbol configuration and the number pilot tones, an 80MHz OFDM symbol will have a number of data tones chosen from the set{216, 228, 230, 232, 234, 236, 238}, according to one embodiment. Inother embodiments, an 80 MHz OFDM symbol has a number of data tones thatis different than values in the set {216, 228, 230, 232, 234, 236, 238}.

With 120 MHz and 160 MHz OFDM symbols, the number of data tones is thecumulative number of data tones in 40 MHz and/or 80 MHz OFDM symbolsthat make up the 120 MHz or 160 MHz OFDM symbol, according to someembodiments.

FIG. 10 is a block diagram of an example pilot system 450. The pilotsystem 450 is utilized in the PHY unit 200 of FIG. 3, according to anembodiment. The PHY unit 200 utilizes another suitable pilot systemdifferent than the pilot system 450 in other embodiments. Referring nowto FIG. 10, the pilot system 450 includes a pilot generator 450 thatgenerates suitable pilot tone values, such as pilot tone valuesdiscussed above or similar pilot tone values. A pilot inserter 458receives the pilot tone values as well as data tones from the spatialmapping unit 236. The pilot inserter 458 inserts the pilot tone valueswithin the data tones at suitable tone indexes to generate an IDFTinput. The IDFT input is then provided to an IDFT unit 240. A pilotcontrol unit 462 generates control signals provided to the pilotgenerator 454 and the pilot inserter 458 to control the number of pilotsgenerated, the tone index positions of the pilot signals, etc. Invarious embodiments, the number and positions of pilots vary accordingto factors such as one or more of the bandwidth of the channel beingutilized (e.g., 20 MHz, 40 MHz, 80 MHz, etc.), channel conditions (e.g.,poor channel conditions may call for more pilots, good channelconditions allow less pilots and therefore higher throughput), etc.

Padding

Padding is utilized is various circumstances, in some embodiments. Forexample, padding is utilized to lengthen a set of information bits to bean input size of a block encoder, in one embodiment. As another example,padding is utilized to lengthen a set of information data to fillentirely an integer number of OFDM symbols in one embodiment. In oneembodiment, padding is utilized both to lengthen a set of informationbits to be an input size of a block encoder, and to lengthen a set ofinformation data to fill entirely an integer number of OFDM symbols.Padding involves adding bits or symbols of a known value or values(e.g., zero or some other suitable value or set of values) to a set ofinformation bits or symbols, in some embodiments. Referring to FIG. 1,in some embodiments, padding is implemented in the MAC unit 18, 28and/or the PHY unit 20, 29.

In some embodiments, padding is implemented with equal rate encoding forpadding bits and data. In one embodiment, padding is implements withseveral additional constraints: 1) an equal number of data bits areinput to each FEC encoder 212 (FIG. 3); 2) a puncturing block at eachFEC encoder 212 operates on an integer number of message blocks, wherethe message block length depends on the code rate; and 3) a total numberof encoded bits fits into an integer number of OFDM symbols.

FIG. 11 is a block diagram of an example padding system, according to anembodiment. The padding system 500 is utilized in conjunction with thePHY unit 200 of FIG. 3, according to an embodiment. In anotherembodiment, another suitable padding system different than the paddingsystem 500 is utilized in conjunction with the PHY unit 200. Referringnow to FIG. 11, the padding system 500 includes a first padding unit 504that receives x bits and adds p₁ padding bits. In one embodiment,padding unit 504 adds the p₁ padding bits so that an equal number ofdata bits will be input to each FEC encoder 212 after parsing by theencoder parser 208. In one embodiment, p₁ is selected according to:

$\begin{matrix}{{p_{1} = {{N_{ES}\left\lceil \frac{x}{N_{ES}} \right\rceil} - x}},} & {{Equ}.\mspace{14mu} 5}\end{matrix}$The padding unit 504 is included in the PHY unit 200 of FIG. 3,according to one embodiment. The padding unit 504 is included in the MACunit 18, 28 of FIG. 1, according to another embodiment.

Referring again to FIG. 11, after parsing by the encoder parser 208,y=(x+p₁)/N_(ES) bits are generated on each output of the encoder parser208, where N_(ES) is the number of FEC encoders 212 being utilized forencoding the information bits. The padding system 500 also includes arespective second padding unit 508 corresponding to each FEC encoder212. The second padding unit 508 receives y bits and adds p₂ paddingbits.

A respective tail bit unit 512 adds N_(tail) tail bits. In oneembodiment, N_(tail) is six. In other embodiments, N_(tail) is asuitable number other than six. The output of the tail bit unit 512 is(y+N_(tail)+p₂) bits. The FEC encoder 212 performs FEC encoding andpuncturing, according to an embodiment, according to a code rate R.Thus, each FEC encoder 212 generates an output having(y+N _(tail) p ₂)*R bits.

In one embodiment, the second padding unit 508 adds the p₂ padding bitsso that the puncturing block at each FEC encoder 212 operates on aninteger number of message blocks, where the message block length dependson the code rate R. In one embodiment, p₂ is selected such that:

$\begin{matrix}{{\frac{\left( {y + N_{tail} + p_{2}} \right)}{R} = k},{k \in I},} & {{Equ}.\mspace{14mu} 6}\end{matrix}$where I is the set of positive integers.

In one embodiment, the second padding unit 508 adds the p₂ padding bitsalso so that a total number of encoded bits fits into an integer numberof OFDM symbols. In one embodiment, p₂ is selected such that:

$\begin{matrix}{{\left( {y + N_{tail} + p_{2}} \right) = {l\left( \frac{{RN}_{CBPS}}{N_{ES}} \right)}},{l \in I},} & {{Equ}.\mspace{14mu} 7}\end{matrix}$where N_(CBPS) is the number of encoded bits per OFDM symbol.

In one embodiment, N_(DBPS) need not be an integer, where N_(DBPS) isthe number of decoded bits per OFDM symbol.

Variables N_(R) and N_(Q) are defined by the simplest rational forms of:

$\begin{matrix}{{R = \frac{N_{R}}{D_{R}}},} & {{Equ}.\mspace{14mu} 8} \\{{\left( \frac{{RN}_{CBPS}}{N_{ES}} \right) = \frac{N_{Q}}{D_{Q}}},} & {{Equ}.\mspace{14mu} 9}\end{matrix}$Then, Equation 6 and Equation 7 can be rewritten as:(y+N _(tail) +p ₂)D _(R) =kN _(R) ,k∈I,  Equ. 10(y+N _(tail) +p ₂)D _(Q) =lN _(Q) ,kΣl,  Equ. 11which imply that:(y+N _(tail) +p ₂)=mLCM(N _(R) ,N _(Q)),  Equ. 12where LCM (a,b) is the least common multiple of a and b. In oneembodiment,

$D_{R} = \left\{ {\begin{matrix}{2,{R = \frac{1}{2}}} \\{3,{R = \frac{2}{3}}} \\{4,{R = \frac{3}{4}}} \\{6,{R = \frac{5}{6}}}\end{matrix}.} \right.$

Therefore, we have:

$\begin{matrix}{{\left( {y + N_{tail} + p_{2}} \right) = {L\; C\;{M\left( {N_{R},N_{Q}} \right)}\left\lceil \frac{y + N_{tail}}{L\; C\; M\;\left( {N_{R},N_{Q}} \right)} \right\rceil}},} & {{Equ}.\mspace{14mu} 13} \\{{p_{2} = {{L\; C\; M\;\left( {N_{R},N_{Q}} \right)\left\lceil \frac{y + N_{tail}}{L\; C\; M\;\left( {N_{R},N_{Q}} \right)} \right\rceil} - \left( {y + N_{tail}} \right)}},} & {{Equ}.\mspace{14mu} 14}\end{matrix}$where ┌a┐ denotes the smallest integer greater than or equal to a.

FIG. 12 is a block diagram of another example padding system 550,according to an embodiment. The padding system 550 is utilized inconjunction with the PHY unit 200 of FIG. 3, according to an embodiment.The PHY unit 200 utilizes another suitable padding system different thanthe padding system 550 in other embodiments. Referring now to FIG. 12,the padding system 550 includes a padding unit 554 that receives x bitsand adds p padding bits, where:p=(p ₁ +N _(ES p2))  Equ. 15The padding unit 554 is included in the PHY unit 200 of FIG. 3,according to one embodiment. The padding unit 554 is included in the MACunit 18, 28 of FIG. 1, according to another embodiment.

Referring again to FIG. 12, after parsing by the encoder parser 208,y=(x+p)/N_(ES) bits are generated on each output of the encoder parser208. The respective tail bit unit 512 adds N_(tail) tail bits. In oneembodiment, N_(tail) is six. In other embodiments, N_(tail) is asuitable number other than six. The output of the tail bit unit 512 is(y+N_(tail)) bits. The FEC encoder 212 performs FEC encoding andpuncturing, according to an embodiment, according to a code rate R.Thus, each FEC encoder 212 generates an output having (y+N_(tail))*Rbits.

Padding is often not limited to a single OFDM symbol. The number of OFDMsymbols, in one embodiment, is determined according to:

$\begin{matrix}{N_{SYM} = {\left\lceil \frac{\left( {\left\lceil \frac{{8L} + N_{service}}{N_{ES}} \right\rceil + N_{tail}} \right)}{W} \right\rceil\frac{{WN}_{ES}}{N_{CBPS}R}}} & {{Equ}.\mspace{14mu} 16}\end{matrix}$where W=LCM (N_(R),N_(Q)), L is a very high throughput (VHT) fieldlength, defined in octets, and N_(service) is a number of service bits.

According to one embodiment, the number of padding bits is determinedaccording to:p=N _(SYM) N _(CBPS) R−(8L+N _(service) +N _(tail) N _(ES))  Equ. 17

When STBC is utilized, constellation points from two consecutive OFDMsymbols are used and mapped into multiple space-time streams spanningtwo OFDM symbols, according to some embodiments. Therefore, with STBC,the number of OFDM symbols should be even. This additional constraint isaccommodated, in one embodiment, by substituting l=2l in Equation 7:

$\begin{matrix}{{\left( {y + N_{tail} + p_{2}} \right) = {2\;{l\left( \frac{{RN}_{CBPS}}{N_{ES}} \right)}}},{l \in I},} & {{Equ}.\mspace{14mu} 18}\end{matrix}$Then, the number of OFDM symbols is given by:

$\begin{matrix}{{N_{SYM} = {\left\lceil \frac{\left( {\left\lceil \frac{{8L} + N_{service}}{N_{ES}} \right\rceil + N_{tail}} \right)}{W} \right\rceil\frac{{WN}_{ES}}{N_{CBPS}R}}},{and}} & {{Equ}.\mspace{14mu} 19}\end{matrix}$where W=LCM (N_(R),N_(Q)) and

${\left( \frac{m_{STBC}{RN}_{CBPS}}{N_{ES}} \right) = \frac{N_{Q}}{D_{Q}}},$and where m_(STBC)=1 if STBC is not used and m_(STBC)=2 if STBC is used.The number of padding bits is determined according to Equation 17.

In another embodiment in which STBC is utilized, a constraint issatisfied:(y+N _(tail) +p ₂)D _(Q)=2jN _(Q) ,j∈I,  Equ. 20Then, the number of OFDM symbols is given by:

$\begin{matrix}{{N_{SYM} = {\left\lceil \frac{\left( {\left\lceil \frac{{8L} + N_{service}}{N_{ES}} \right\rceil + N_{tail}} \right)}{W} \right\rceil\frac{{WN}_{ES}}{N_{CBPS}R}}},{and}} & {{Equ}.\mspace{14mu} 21}\end{matrix}$where W=LCM (N_(R),2N_(Q)). The number of padding bits is determinedaccording to Equation 17.

In some scenarios, for example some MCS/number of encoders/packet lengthscenarios, the embodiments described above will result in a large numberof padding bits and hence a large number of dummy OFDM symbols. Forinstance, when a puncturing block does not see an integer number ofblocks or when N_(CBPS) is not a multiple of N_(ES), a large number ofpadding bits may result.

In some embodiments, bits at the end portion of a packet are encodedwith a code rate different than a code rate utilized at the remainingportion of the packet. In one embodiment, bits at the end portion of thepacket are encoded at a smallest rate, e.g., a 1/2 convolutional code(message block length of one). This helps to ensure that a puncturingblock at each FEC encoder 212 operates on an integer number of messageblocks. In one embodiment, an entire packet is encoded with a 1/2convolutional code, and then puncturing is performed on a first portionof the packet to achieve a desired coding rate, whereas no puncturing isperformed of the end portion of the packet. In one embodiment, paddingin a MAC unit is applied prior to encoding the PHY packet such that theend portion of the packet is encoded with a code rate different than acode rate utilized at the remaining portion of the packet.

In one embodiment, a number of tones and allowable MCS's are selectedsuch that the following constraints are satisfied: 1) for rates 1/2,3/4, and 5/6,

${mod}\left( {\frac{N_{CBPS}}{N_{ES}},D_{R}} \right)$is even, which requires

$\frac{N_{CBPS}}{N_{ES}}$to be an integer; and 2) for rate 2/3, we ensure that

$\frac{N_{CBPS}}{N_{ES}D_{R}}$is an integer. In this embodiment, the number of OFDM symbols is givenby:

$\begin{matrix}{N_{SYM}\left\lceil \frac{\left( {\left\lceil \frac{{8L} + N_{service}}{N_{ES}} \right\rceil + N_{tail}} \right)N_{ES}}{m_{STBC}{RN}_{CBPS}} \right\rceil m_{STBC}} & {{Equ}.\mspace{14mu} 22}\end{matrix}$In this embodiment, the number of padding bits is given by:

$\begin{matrix}{p = {\left( {{\left\lfloor \frac{N_{SYM}N_{CBPS}}{N_{ES}D_{R}} \right\rfloor N_{R}N_{ES}} + {\frac{{mod}\left( {\frac{N_{SYM}N_{CBPS}}{N_{ES}},D_{R}} \right)}{2}N_{ES}}} \right) - \left( {{8L} + N_{service} + {N_{tail}N_{ES}}} \right)}} & {{Equ}.\mspace{14mu} 23}\end{matrix}$

In some embodiments, padding bits are added after encoding, such as whena preamble of a packet includes an indicator of the number of bits inthe packet. In one embodiment, the number of OFDM symbols when paddingoccurs after encoding is given by:

$\begin{matrix}{N_{SYM} = {\left\lceil \frac{\left( \left\lceil \frac{{8L} + N_{service} + {N_{tail}N_{ES}}}{N_{ES}N_{R}} \right\rceil \right)N_{ES}N_{R}}{m_{STBC}{RN}_{CBPS}} \right\rceil m_{STBC}}} & {{Equ}.\mspace{14mu} 24}\end{matrix}$In this embodiment, the number of padding bits after encoding is givenby:

$\begin{matrix}{p_{after} = {{N_{SYM}N_{CBPS}} - {\left( \left\lceil \frac{{8L} + N_{service} + {N_{tail}N_{ES}}}{N_{ES}N_{R}} \right\rceil \right)N_{ES}D_{R}}}} & {{Equ}.\mspace{14mu} 25}\end{matrix}$In this embodiment, the number of padding bits before encoding is givenby:

$\begin{matrix}{p_{before} = {{\left( \left\lceil \frac{{8L} + N_{service} + {N_{tail}N_{ES}}}{N_{ES}N_{R}} \right\rceil \right)N_{ES}D_{R}} - \left( {{8L} + N_{service} + {N_{tail}N_{ES}}} \right)}} & {{Equ}.\mspace{14mu} 26}\end{matrix}$

In an embodiment, padding bits are added before encoding to ensure thateach encoder has the same number of bits, and to ensure that the encodersees an integer number of puncture patterns. Additionally in thisembodiment, padding bits are added after encoding.

In embodiments in which padding bits are added after encoding, packetlength information is provided to the receiver to enable decoding of theinformation. In one embodiment, the packet length information isprovided in a PHY data unit preamble. For example, the packet lengthinformation provided in the PHY data unit preamble is indicated in termsof OFDM symbols. In another embodiment, the packet length information isprovided using MAC layer signaling.

FIG. 13 is a block diagram of another example padding system 600,according to an embodiment. The padding system 600 is utilized inconjunction with the PHY unit 200 of FIG. 3, according to an embodiment.The PHY unit 200 utilizes another suitable padding system different thanthe padding system 600 in other embodiments. Referring now to FIG. 13,the padding system 550 includes a first padding unit 604 that addsP_(before) padding bits. The padding unit 604 is included in the PHYunit 200 of FIG. 3, according to one embodiment. The padding unit 604 isincluded in the MAC unit 18, 28 of FIG. 1, according to anotherembodiment. In one embodiment, MAC unit padding is provided up to a32-bit or 8-bit boundary.

Referring again to FIG. 13, after parsing by the encoder parser 208, arespective tail bit unit 608 adds N_(tail) tail bits. After the FECencoder 212, a second padding unit 612 adds P_(after) padding bits.

In some embodiments, MCS's are chosen based on whether one or moreconditions corresponding to padding are satisfied. In particular, if theconditions are not satisfied for a particular MCS, the MCS is notutilized for transmission. For example, in one embodiment, only MCS'sare utilized that satisfy:

$\begin{matrix}{{{{mod}\left( {\frac{N_{CBPS}}{N_{ES}},D_{R}} \right)} = 0},} & {{Equ}.\mspace{14mu} 27}\end{matrix}$which implies that

$\frac{N_{DBPS}}{N_{ES}}\mspace{14mu}{and}\mspace{14mu}\frac{N_{CBPS}}{N_{ES}}$are integers. Then, the number of OFDM symbols, according to anembodiment, is determined by:

$\begin{matrix}{N_{SYM} = {m_{STBC}\left\lceil \frac{{8L} + N_{service} + {N_{tail}N_{ES}}}{m_{STBC}N_{DBPS}} \right\rceil}} & {{Equ}.\mspace{14mu} 28}\end{matrix}$

The number of padding bits, according to an embodiment, is determinedby:p=N _(SYM) N _(DBPS)−8L−N _(service) −N _(tail) N _(ES)  Equ. 29To satisfy Equation 27, all MCS/encoder combinations cannot beaccommodated, according to an embodiment. In one embodiment, MCS entriesin an MCS table are excluded from consideration if Equation 27 is notsatisfied. In another embodiment, one MCS table is utilized, and anindex to the table is interpreted differently depending on the channelbandwidth so that certain MCS entries are excluded from considerationfor certain channel bandwidths.

In embodiments of padding techniques discussed above, it is assumed thatthe encoder parser 208 (FIG. 3) assigns one bit to each encoder in around robin fashion. Additionally, in the embodiments of paddingtechniques discussed above, it is assumed that after padding, eachencoder has an equal number of input bits. In some embodiments, theencoder parser 208 (FIG. 3) is configured to parse bits to differentencoders such that the number of bits parsed to each encoder is not thesame for all encoders, in some situations. In these embodiments, theencoder parser 208 is configured so that the puncturing block at eachFEC encoder 212 operates on an integer number of message blocks, wherethe message block length depends on the code rate. In one embodiment,the encoder parser 208 assigns N_(R) bits to each encoder 212 in a roundrobin fashion, where N_(R) can be more than one.

In some embodiments, only MCS's are utilized that correspond to bothN_(DBPS) and N_(CBPS) being integers. For instance, in one embodiment,MCS entries in an MCS table are excluded from consideration when they donot correspond to both N_(DBPS) and N_(CBPS) being integers. In anotherembodiment, one MCS table is utilized, and an index to the table isinterpreted differently depending on the channel bandwidth so thatcertain MCS entries are excluded from consideration for certain channelbandwidths. In one embodiment, the number of symbols is determinedaccording to Equation 28 and the number of padding bits is determinedaccording to Equation 29. Referring to FIG. 3, in one embodiment, theencoder parser 208 is configured to handle situations in which

$\frac{N_{CBPS}}{N_{ES}}$is not an integer, i.e., some encoders might receive fewer bits thanothers and thus the number of bits parsed to each encoder is not thesame for all encoders. In these embodiments, fewer MCS's are excluded ascompared to the constraint of Equation 27.

In other embodiments, only MCS's are utilized that correspond to both 1)N_(ES) is a multiple of N_(R); and 2) N_(CBPS) is not a multiple ofN_(R). For instance, in one embodiment, MCS entries in an MCS table areexcluded from consideration when they do not correspond to both 1)N_(ES) is a multiple of N_(R); and 2) N_(CBPS) is not a multiple ofN_(R). An example of an MCS that is excluded in one embodiment is 256QAM, 3/4 coding rate, and with 3 binary convolutional coding encoders.This is just one example of the exclusion of a particular MCS. Moregenerally, MCSs are excluded based particular suitable criteria relatedto padding, such as described above. In another embodiment, one MCStable is utilized, and an index to the table is interpreted differentlydepending on the channel bandwidth so that certain MCS entries areexcluded from consideration for certain channel bandwidths. Thus, inthese embodiments, a particular MCS is allowable for one or more firstchannel bandwidths, but is excluded for one or more second channelbandwidths. For example, a particular MCS is allowable for a 120 MHzchannel bandwidth, but is excluded for 80 MHz and 160 MHz bandwidths.This is merely an example, and other MCSs are allowable with another setof one or more first channel bandwidths but excluded for another set ofone or more second channel bandwidths.

In one embodiment, packets transmitted according to the firstcommunication protocol have an aggregated MAC protocol data unit(A-MPDU) frame format. FIG. 14 is a diagram of an example A-MPDU 650,according to an embodiment. The A-MPDU is generated so that it is amultiple of K bytes, where K is one or four, according to someembodiments. The MAC unit 18, 28 (FIG. 1) is configured to generate theA-MPDU of FIG. 14, in one embodiment. Also, the MAC unit 18, 28 (FIG. 1)is configured to add zero, one, or more K byte MAC delimiters, accordingto an embodiment. The PHY unit 20, 29 (FIG. 1) is configured to add tailbits and then append padding bits (for example, of value zero) from theend of the last 32-bit boundary, according to an embodiment.

In some embodiments, independent data corresponding to differentstations are transmitted simultaneously, which is hereby referred to asmulti-user transmissions. See, for example, U.S. patent application Ser.No. 12/758,603, filed on Apr. 12, 2010, and entitled “Physical LayerFrame Format for WLAN,” which is hereby incorporated by reference hereinin its entirety; U.S. patent application Ser. No. 12/175,526, filed onJul. 18, 2008, and entitled “Access Point with Simultaneous DownlinkTransmission of Independent Data for Multiple Client Stations,” which ishereby incorporated by reference herein in its entirety; and U.S. patentapplication Ser. No. 12/175,501, filed on Jul. 18, 2008, and entitled“Wireless Network with Simultaneous Uplink Transmission of IndependentData from Multiple Client Stations,” which is hereby incorporated byreference herein in its entirety.

In some embodiments having multi-user transmissions, each packetcorresponding to a particular user is padded to a length correspondingto the longest packet in the simultaneous transmission. Thus, in theseembodiments, the number of padding bits for a particular user iscalculated based on a number of symbols in the longest packet in thesimultaneous transmission. In an example scenario with K users, this isexpressed as:N _(SYM) ^(max)=max(N _(SYM) ^(user1) ,N _(SYM) ^(user2) , . . . ,N_(SYM) ^(userK))  Equ. 30where N_(SYM) ^(userk) is the number of symbols (including padding bits)required if only the packet corresponding to the k-th user were beingtransmitted. In an embodiment, the number of padding bits for the k-thuser is then calculated based on:p ^(userk) =N _(SYM) ^(max) N _(CBPS) ^(userk) R ^(userk)−(8L ^(userk)+N _(service) +N _(tail) N _(ES) ^(userk))  Equ. 31In various embodiments, padding is performed in the PHY unit 20, 29and/or the MAC unit 18, 28. In an embodiment in which the packet lengthis specified in the PHY preamble, padding is performed in the PHY unit20, 29.

In one embodiment having multi-user transmissions, the number of symbolsin the multi-user packet is chosen such that the following conditionsare satisfied for all users participating in the transmission:(N _(SYM) ^(max) −N _(SYM) ^(userk) is a multiple of m _(STBC) ^(userk),and(N _(SYM) ^(max) −N _(SYM) ^(userk))N _(CBPS) ^(userk) is a multiple ofN _(ES) ^(userk) D _(R) ^(userk), andIn a special case where N_(CBPS) ^(userk) is a multiple of N_(ES)^(userk) D_(R) ^(userk)∀k, the number of symbols in the multi-userpacket is given by:

$\begin{matrix}{N_{SYM}^{\max} = {\left\lceil \frac{\max\left( {N_{SYM}^{{user}\; 1},N_{SYM}^{{user}\; 2},\ldots\mspace{11mu},N_{SYM}^{userK}} \right)}{m_{STBC}} \right\rceil m_{STBC}}} & {{Equ}.\mspace{14mu} 32}\end{matrix}$

where m_(STBC)=1 if none of the k users utilize STBC, and m_(STBC)=2 ifat least one of the k users utilizes STBC. The number of padding bitsfor the k-th user is given by Equation 31.

As discussed above, in some embodiments, bits at the end portion of apacket are encoded with a code rate different than a code rate utilizedat the remaining portion of the packet. In one embodiment, bits at theend portion of the packet are encoded at a smallest rate, e.g., a 1/2convolutional code (message block length of one). In some embodimentswith multi-user transmissions, the number of symbols in the multi-userpacket is given by Equation 32, and the number of padding bits for thek-th user is given by:

$\begin{matrix}{p^{userk} = {\left( {{\left\lfloor \frac{N_{SYM}^{\max}N_{CBPS}^{userk}}{N_{ES}^{userk}D_{R}^{userk}} \right\rfloor N_{R}^{userk}N_{ES}^{userk}} + {\frac{{mod}\left( {\frac{N_{SYM}^{\max}N_{CBPS}^{userk}}{N_{ES}^{userk}},D_{R}^{userk}} \right)}{2}N_{ES}^{userk}}} \right) - \left( {{8L^{userk}} + N_{service} + {N_{tail}N_{ES}^{userk}}} \right)}} & {{Equ}.\mspace{14mu} 33}\end{matrix}$

As discussed above, in some embodiments, padding bits are added afterencoding, such as when a preamble of a packet includes an indicator ofthe number of bits in the packet. In some embodiments with multi-usertransmissions, the number of symbols in the multi-user packet is givenby Equation 32, and the number of padding bits (after encoding) for thek-th user is given by:

$\begin{matrix}{P_{after}^{userk} = {{N_{SYM}^{\max}N_{CBPS}^{userk}} - {\left( \left\lceil \frac{{8L} + N_{service} + {N_{tail}N_{ES}^{userk}}}{N_{ES}^{userk}N_{R}^{userk}} \right\rceil \right)N_{ES}^{userk}D_{R}^{userk}}}} & {{Equ}.\mspace{14mu} 34}\end{matrix}$In these embodiments, the packet length of each user packet is specifiedseparately in portions of the PHY preambles corresponding to the users(e.g., in the VHT-SIG fields corresponding to the users). The number ofpadding bits before encoding is provided by Equation 26, in anembodiment.

In one embodiment, MAC padding is utilized for multi-user transmissions,and PHY padding is used for single-user transmissions.

In some embodiments of padding techniques such as discussed above, sometechniques may result in an excessive number of padding bits and/ordummy OFDM symbols for certain MCS and number of FEC encoderscombinations. In some embodiments, such combinations are avoided byexcluding certain MCS and number of FEC encoders combinations from useby the PHY unit 19, 29. For example, if a table of MCS and number of FECencoders entries, certain entries are excluded, in an embodiment. Inanother embodiment, one MCS table is utilized, and an index to the tableis interpreted differently depending on the channel bandwidth so thatcertain MCS entries are excluded from consideration for certain channelbandwidths. For instance, in one embodiment, only MCS's are consideredfor use in which

$\frac{N_{CBPS}}{N_{ES}},$N_(DBPS),

$\frac{N_{CBPS}}{N_{P\_ OUT}R}\mspace{14mu}{and}\mspace{14mu}\frac{N_{CBPS}}{N_{ES}N_{P\_ OUT}}$are integers, where N_(P) _(_) _(OUT) is the number of bits output bythe puncturing block of the FEC encoder. In other embodiments, othersuitable conditions are utilized to exclude MCS and number of FECencoders combinations to avoid excessive numbers of padding bits and/ordummy OFDM symbols.

In some embodiments, the type of padding is different based on thebandwidth of the packet. For example, in embodiments that utilize an MCStable, the set of allowed MCS entries is dependent on the packetbandwidth. In other embodiments, some MCS's are excluded for multi-userpackets, whereas the same MCS's are allowed, at least for some packetbandwidths, for single user packets. In some embodiments utilizingmulti-user transmissions, different MCS's are allowed based on thenumber of users. In some embodiments that utilize an MCS table, the setof allowed MCS entries is dependent on the packet bandwidth, whether thetransmission is part of a multi-user transmission, and/or the number ofusers in a multi-user transmission. In another embodiment, one MCS tableis utilized, and an index to the table is interpreted differentlydepending on the channel bandwidth, whether the transmission is part ofa multi-user transmission, and/or the number of users in a multi-usertransmission, so that certain MCS entries are excluded fromconsideration for certain combinations of channel bandwidth, whether thetransmission is part of a multi-user transmission, and/or the number ofusers in a multi-user transmission.

In some embodiments and scenarios, the bits output by the puncturingblock of an FEC encoder lie at an OFDM symbol boundary and overlap withthe next OFDM symbol. This is different than in the IEEE 802.11nStandard, where N_(CBPS) is always a multiple of N_(P) _(_) _(OUT). Inthese embodiments, the receiver PHY unit is configured to handle bitsoutput by the puncturing block of an FEC encoder lie at an OFDM symbolboundary and overlap with the next OFDM symbol, which requires suitablebuffering capability in some embodiments.

As discussed above, in some embodiments, N_(tail) is six. In someembodiments, N_(tail) is a suitable value other than six. For example,in some embodiments, N_(tail) is zero.

In some embodiments, N_(service) is the same as specified in the IEEE802.11n Standard. In other embodiments, N_(service) is a suitable valueother than as specified in the IEEE 802.11n Standard.

In some embodiments, the padding bits are placed before the tail bits,and padding bits and tail bits are scrambled together. In otherembodiments, all or a portion of padding bits are placed after the tailbits. With multiple FEC encoders and when all or a portion of paddingbits are placed after the tail bits, the encoder parser 208 (FIG. 3) isconfigured to distribute padding bits equally amongst the FEC encoders212, according to an embodiment.

In one embodiment, for OFDM symbols with 234 tones per 80 MHz, and 450Mbps data rate per encoder, the MCS (64-QAM, 3/4, N_(SS)=3, N_(ES)=2) isexcluded for 80 MHz channels and 160 MHz channels, but is allowed for120 MHz channels. This is just one example of the exclusion of aparticular MCS. More generally, MCSs are excluded based particularsuitable criteria related to padding, such as described above. Inanother embodiment, some 256-QAM rates are excluded for 120 MHz and 160MHz channels.

In one embodiment, an MCS combination is excluded for all20/40/80/120/160 channel bandwidths as long as the MCS combinationviolates an exclusion rule for at least one of the 20/40/80/120/160channel bandwidths. In another embodiment, a single MCS table is sharedfor all of or at least multiple ones of 20/40/80/120/160 channelbandwidths, but the MCS index is interpreted differently for differentcombinations of one or more of channel bandwidths, whether thetransmission is part of a multi-user transmission, and/or the number ofusers in a multi-user transmission.

In one embodiment, the MAC unit 18, 28 computes N_(SYM) and p (thenumber of padding bits). Then, the MAC unit 18, 28 pads to k-bitboundary (e.g., k=8 or 32) of the overall p padding bits (e.g., pad bitsset to zero or some other suitable value or set of values). The MAC unit18, 28 sends a signal to the PHY unit 19, 29 (e.g., by a TxVector) thatindicates the PHY unit 19, 29 is to add remaining padding bits. In thisembodiment, BCC tail bits are inserted after padding bits.

Stream Parser

Referring again to FIG. 3, the stream parser 216 divides encoded bitstreams into individual spatial streams, which are then separatelyinterleaved and mapped into constellation points, according to anembodiment. In one embodiment, the stream parser 216 operates in amanner similar to the stream parser specified in the IEEE 802.11nStandard. In one embodiment, the stream parser uses the output of eachFEC encoder 212 in a round robin fashion using S bits from each FECencoder 212 each cycle, where:

$\begin{matrix}{S = {\sum\limits_{i = 1}^{N_{SS}}\;{\max\left\{ {1,\frac{N_{BPSCS}\left( i_{SS} \right)}{2}} \right\}}}} & {{Equ}.\mspace{14mu} 35}\end{matrix}$where N_(BPSCS)(i_(SS)) is the number of coded bits per carrier forspatial stream i_(SS).

Interleaver

In an embodiment, each interleaver 220 divides the bits per symbol ineach spatial stream into blocks of size N_(ROW)×N_(COL). In oneembodiment, bits in each block are entered into a matrix of sizeN_(ROW)×N_(COL) on a row by row basis and read out along the columns ofthe matrix. This operation is represented by:i=N _(ROW)(k mod N _(COL))+floor(k/N _(COL))k=0,1, . . . ,N _(CBPSS)(i_(SS))−1   Equ. 36where i and k represent the output and input bit indices, andN_(CBPSS)(i_(SS)) is the number of coded bits per symbol for the i-thspatial stream, as defined in the IEEE 802.11n Standard.

In another embodiment, in order to map adjacent coded bits to less andmore significant constellation bits, the interleaver operation isrepresented by:

$\begin{matrix}{{j = {{{s\left( i_{SS} \right)}{{floor}\left( {i/{s\left( i_{SS} \right)}} \right)}} + {\left( {i + {N_{CBPSS}\left( i_{SS} \right)} - {{floor}\left( \frac{{iN}_{COL}}{N_{CBPSS}\left( i_{SS} \right)} \right)}} \right)\;{mod}\mspace{11mu}{s\left( i_{SS} \right)}}}}\mspace{20mu}{{i = 0},1,\ldots\mspace{11mu},{{N_{CBPSS}\left( i_{SS} \right)} - 1}}} & {{Equ}.\mspace{14mu} 37}\end{matrix}$where j and i represent the output and input bit indices.

In yet another embodiment, in order to separate adjacent coded bits inthe spatial domain, each stream is cyclically rotated via a frequencyrotation parameter N_(ROT):

$\begin{matrix}{{r = {\left( {j - {\left( {{\left( {\left( {i_{SS} - 1} \right)2} \right){mod}\; 3} + {3\;{{floor}\left( \frac{i_{SS} - 1}{3} \right)}}} \right)N_{ROT}{N_{BPSCS}\left( i_{SS} \right)}}} \right){mod}\mspace{11mu}{N_{CBPSS}\left( i_{SS} \right)}}}\mspace{20mu}{{j = 0},1,\ldots\mspace{11mu},{{N_{CBPSS}\left( i_{SS} \right)} - 1}}} & {{Equ}.\mspace{14mu} 38}\end{matrix}$

In still another embodiment, in order to separate adjacent coded bits inthe spatial domain, each stream is cyclically rotated via a frequencyrotation parameter N_(ROT):r=(j−f(i _(SS) ,N _(SS))N _(ROT) N _(BPSCS)(i _(SS)))mod N _(CBPSS)(i_(SS))j=0,1, . . . ,N _(CBPSS)(i _(SS))−1  Equ. 39where f(i_(SS),N_(SS)) is a suitable function of both the spatial streamindex and the total number of spatial streams.

In one embodiment, f(i_(SS),N_(SS)=8) is given by Table 1.

TABLE 1 i_(SS) 1 2 3 4 5 6 7 8 f (i_(SS), N_(SS) = 8) 0 3 6 1 4 7 2 5

In another embodiment, f(i_(SS),N_(SS)=6) is given by Table 2.

TABLE 2 i_(SS) 1 2 3 4 5 6 f (i_(SS), N_(SS) = 6) 0 2 4 1 5 3

For a given tone mapping, interleaver parameters are the number of rows,N_(ROW), the number of columns, N_(COL), and the frequency rotationparameter, N_(ROT), according to an embodiment. In one embodiment, thevalues of N_(ROW) and N_(COL) satisfy the relationship:N _(ROW) N _(COL) =N _(VHT−Data) ^(Tone) N _(BPSCS)(i)  Equ. 40for any i, where N_(VHT−Data) ^(Tone) is the number of data tones, andN_(BPSCS)(i) is the number of coded bits per carrier for the i-thspatial stream. FIG. 15 is a table providing some example values for theinterleaver parameters, according to one embodiment.

In some embodiments, N_(ROT) varies depending on the number of streams.For example, in one embodiment:N _(ROT) =g(N _(SS))  Equ. 41where g (N_(SS)) is a function of the number of spatial streams. In oneembodiment:

$\begin{matrix}{N_{ROT} = \frac{N_{{VHT} - {Data}}^{Tone}}{N_{SS}}} & {{Equ}.\mspace{14mu} 42}\end{matrix}$In another embodiment:

$\begin{matrix}{N_{ROT} = {\frac{N_{{VHT} - {Data}}^{Tone}}{N_{SS}} + c}} & {{Equ}.\mspace{14mu} 43}\end{matrix}$where c is a suitable integer constant.

Examples of N_(ROT) values for five to eight spatial streams, accordingto an embodiment, is provided in the table of FIG. 16.

In the IEEE 802.11n Standard, N_(COL) is the same for all modulationschemes (i.e., independent of constellation size) while N_(ROW) is alinear function of constellation size. In one embodiment, both N_(COL)and N_(ROW) vary as the modulation scheme varies. In other words,N_(COL) will have at least two different values depending on theparticular modulation scheme, and N_(ROW) will have at least twodifferent values depending on the particular modulation scheme. Forexample, in one embodiment, both N_(COL) and N_(ROW) vary as theconstellation size varies. In other words, N_(COL) will have at leasttwo different values depending on the particular constellation size, andN_(ROW) will have at least two different values depending on theparticular constellation size. In one embodiment, N_(COL) and N_(ROW)are defined as:N _(ROW) =f ₁(N _(BPSCS)(i))  Equ. 44N _(COL) =f ₂(N _(BPSCS)(i))  Equ. 45where f₁ and f₂ are mappings defined from N_(BPSCS)(i) to arbitrarynumbers such that:N _(COL) =N _(VHT−Data) ^(Tone) N _(BPSCS)(i)  Equ. 46

In one embodiment, f₁ and f₂ are non-linear functions. An example foreight pilot tones in an 80 MHz channel (assuming 234 data tones),according to an embodiment, is provided in Table 3.

TABLE 3 N_(BPSCS)(i) N_(ROW), N_(COL) 1 (BPSK) (18, 13) 2 (QPSK) (36,13) 4 (16-QAM) (36, 26) 6 (64-QAM) (54, 26) 8 (256-QAM) (72, 26)

The example of Table 3 illustrates that N_(ROW) sometimes is the samefor different size constellations (e.g., QPSK and 16-QAM). Inparticular, N_(ROW) has four different values for five differentconstellation sizes. The example of Table 3 also illustrates thatN_(COL) sometimes varies for different size constellations (e.g.,BPSK/QPSK versus 16-QAM/64-QAM/256-QAM). In particular, N_(COL) has twodifferent values for five different constellation sizes. In one specificexample, in an 80 MHz channel (assuming 234 data tones), N_(ROW),N_(COL) is (9*N_(BPSCS)(i_(SS)), 26). In another example, an 80 MHzchannel (assuming 234 data tones), N_(ROW), N_(COL) is(6*N_(BPSCS)(i_(SS)), 39).

FIG. 17 is a flow diagram of an example method 750 for generating afirst OFDM symbol for transmission via a communication channel having afirst bandwidth, according to an embodiment. The PHY unit 20, 29(FIG. 1) is configured to implement the method 750, in one embodiment.Similarly, the PHY unit 200 (FIG. 3) is configured to implement themethod 750, in another embodiment. In other embodiments, anothersuitable PHY unit is configured to implement the method 750.

The method 750 of FIG. 17 will be described with respect to FIGS. 5B,7A, and 7B for ease of explanation. OFDM symbols generated according tothe method 750, however, need not have the example OFDM symbol structureof FIG. 5B, 7A, or 7B.

At block 754, a first frequency portion of the first OFDM symbol isgenerated, where the first frequency portion of the first OFDM symbolhas a structure corresponding to a structure of a second OFDM symbolhaving a bandwidth equal to a bandwidth of the first frequency portionof the first OFDM symbol. For example, the first frequency portion ofthe first OFDM symbol has guard tones, null tones, and direct current(DC) tones that correspond to guard tones and DC tones of the secondOFDM symbol, in an embodiment. Referring to FIGS. 5B and 7A, the OFDMsymbol 330 has a bandwidth of 40 MHz and is for transmission in a 40 MHzwide communication channel, whereas the OFDM symbol 390 has a bandwidthof 80 MHz and is for transmission in an 80 MHz wide communicationchannel. The lower half (in frequency) of the OFDM symbol 390 has astructure that corresponds to the structure of the OFDM symbol 330. Forexample, the lower (in frequency) guard tones of the OFDM symbol 390correspond to the lower (in frequency) guard tones of the OFDM symbol330. The guard tones at indexes −5 through −1 of the OFDM symbol 390correspond to the upper (in frequency) guard tones of the OFDM symbol330. The three null tones of the lower (in frequency) half of the OFDMsymbol 390 correspond to the DC tones of the OFDM symbol 330.

Referring now to FIGS. 5B and 7B, the lower 40 MHz sideband of the OFDMsymbol 410 has a structure that corresponds to the structure of the OFDMsymbol 330 in a manner similar to that described above with respect toFIGS. 5B and 7A.

At block 758, a second frequency portion of the first OFDM symbol isgenerated, where the second frequency portion of the first OFDM symbolhas a structure corresponding to the structure of the second OFDMsymbol. For example, the second frequency portion of the first OFDMsymbol has guard tones, null tones, and direct current (DC) tones thatcorrespond to guard tones and DC tones of the second OFDM symbol.Referring to FIGS. 5B and 7A, the OFDM symbol 330 has a bandwidth of 40MHz and is for transmission in a 40 MHz wide communication channel,whereas the OFDM symbol 390 has a bandwidth of 80 MHz and is fortransmission in an 80 MHz wide communication channel. The upper half (infrequency) of the OFDM symbol 390 has a structure that corresponds tothe structure of the OFDM symbol 330. For example, the upper (infrequency) guard tones of the OFDM symbol 390 correspond to the upper(in frequency) guard tones of the OFDM symbol 330. The guard tones atindexes 0 through 5 of the OFDM symbol 390 correspond to the lower (infrequency) guard tones of the OFDM symbol 330. The three null tones ofthe upper (in frequency) half of the OFDM symbol 390 correspond to theDC tones of the OFDM symbol 330.

Referring now to FIGS. 5B and 7B, the upper 40 MHz sideband of the OFDMsymbol 410 has a structure that corresponds to the structure of the OFDMsymbol 330 in a manner similar to that described above with respect toFIGS. 5B and 7A.

As another example, a 160 MHz bandwidth OFDM symbol can be generatedaccording to an embodiment of the method 750 based on the structure ofan 80 MHz OFDM symbol such as any one of the example OFDM symbols ofFIGS. 6A, 6B, and 7A.

In another embodiment, the method 750 further includes generating athird frequency portion of the first OFDM symbol, where the thirdfrequency portion of the first OFDM symbol has a structure correspondingto the structure of the second OFDM symbol. For example, a 120 MHzbandwidth OFDM symbol can be generated, according to an embodiment ofthe method 750, having three portions based on the structure of a 40 MHzOFDM symbol such as any either of the example OFDM symbols of FIGS. 5Aand 5B.

In other embodiments, the method 750 further includes generating atleast a fourth frequency portion of the first OFDM symbol in a mannersimilar to those discussed above.

In some embodiments, the method 750 is utilized for generatingnon-contiguous (in frequency) OFDM symbols, whereas a different methodis utilized for generating contiguous (in frequency) OFDM symbols. Inthese embodiments, an upper portion and a lower portion of a contiguousOFDM symbol need not have a structure that corresponds to another OFDMsymbol having the same bandwidth as the portion.

FIG. 18 is a flow diagram of an example method 800 for generating a PHYdata unit for transmission via a communication channel, according to anembodiment. The PHY unit 20, 29 (FIG. 1) is configured to implement themethod 800 at least partially, in one embodiment. Similarly, the PHYunit 200 (FIG. 3) is configured to implement the method 800 at leastpartially, in another embodiment. In other embodiments, another suitablePHY unit is configured to implement the method 800 at last partially.

At block 804, 1) a number of FEC encoders, 2) an MCS, and 3) a number ofspatial streams to be utilized in transmitting the PHY data unit aredetermined. At block 808, a number of padding bits is determined sothat, after adding the padding bits, after FEC encoding, and aftermodulation, encoded information bits and padding bits fit within aninteger number of OFDM symbols. Determining the number of padding bitsincludes determining the integer number of OFDM symbols based on LCM(N_(R),N_(Q)). For example, the number of OFDM symbols is determinedaccording to one or more of Equations 16, 19, 21, and 22, according tosome embodiments, or another suitable equation. After determining thenumber of OFDM symbols, the number of padding bits is determinedaccording Equation 17, in an embodiment, or another suitable equation.

At block 812, the padding bits are added to the information bits. Someor all of the padding bits are added to the information bits beforeencoder parsing, according to some embodiments. For instance, in oneembodiment, some or all of the padding bits are added to the informationbits by a padding system of the MAC unit 18, 28 (FIG. 1). In oneembodiment, some or all of the padding bits are added to the informationbits after encoder parsing. The block 812 is implemented at least partlyby the padding system 500 (FIG. 11) or the padding system 550 (FIG. 12),in some embodiments, or by another suitable padding system.

At block 816, the information bits are encoded by the number of FECencoders determined at block 804 and according to the MCS determined atblock 804. Block 816 includes parsing the information bits to the FECencoders. In some embodiments, a transmitter includes four or more FECencoders, and a number of the FEC encoders to be utilized is determinedbased on channel conditions, capabilities of a receiver, etc., forexample. In one embodiment, block 816 is implemented by the encoderparser 208 and one or more of the FEC encoders 212 (FIG. 3).

At block 820, the encoded information bits are modulated according tothe MCS determined at block 804. Block 820 is implemented by one or moreof the constellation mappers 224 (FIG. 3), according to an embodiment.

At block 824, one or more OFDM symbols are formed. In one embodiment,block 824 is implemented at least partially by one or more of the IDFTunits 240 and one or more of the GI and window units 244 (FIG. 3).

FIG. 19 is a flow diagram of another example method 850 for generating aPHY data unit for transmission via a communication channel, according toanother embodiment. The PHY unit 20, 29 (FIG. 1) is configured toimplement the method 850 at least partially, in one embodiment.Similarly, the PHY unit 200 (FIG. 3) is configured to implement themethod 850 at least partially, in another embodiment. In otherembodiments, another suitable PHY unit is configured to implement themethod 850 at last partially.

At block 854, padding bits are added to information bits to generatepayload information. Some or all of the padding bits are added to theinformation bits before encoder parsing, according to some embodiments.For instance, in one embodiment, some or all of the padding bits areadded to the information bits by a padding system of the MAC unit 18, 28(FIG. 1). In one embodiment, some or all of the padding bits are addedto the information bits after encoder parsing. The block 854 isimplemented at least partly by the padding system 500 (FIG. 11) or thepadding system 550 (FIG. 12), in some embodiments, or by anothersuitable padding system.

At block 858, a first portion of the payload information is encoded byone or more FEC encoders according to first code rate. Block 858includes parsing payload information to the one or more FEC encoders. Inone embodiment, block 858 is implemented by the encoder parser 208 andone or more of the FEC encoders 212 (FIG. 3).

At block 862, a second portion of the payload information is encoded byone or more FEC encoders according to second code rate. In oneembodiment, the second code rate is a lowest code rate of the one ormore FEC encoders. In one embodiment, the second code rate is a lowercode as compared to the first code rate. Block 862 includes parsingpayload information to the one or more FEC encoders. In one embodiment,block 862 is implemented by the encoder parser 208 and one or more ofthe FEC encoders 212 (FIG. 3).

At block 866, the encoded payload information is modulated. Block 866 isimplemented by one or more of the constellation mappers 224 (FIG. 3),according to an embodiment.

At block 870, one or more OFDM symbols are formed. In one embodiment,block 870 is implemented at least partially by one or more of the IDFTunits 240 and one or more of the GI and window units 244 (FIG. 3).

FIG. 20 is a flow diagram of another example method 900 for generating aPHY data unit for transmission via a communication channel, according toanother embodiment. The PHY unit 20, 29 (FIG. 1) is configured toimplement the method 900 at least partially, in one embodiment.Similarly, the PHY unit 200 (FIG. 3) is configured to implement themethod 900 at least partially, in another embodiment. In otherembodiments, another suitable PHY unit is configured to implement themethod 900 at last partially.

At block 904, zero or more first padding bits are added to informationbits. Some or all of the first padding bits are added to the informationbits before encoder parsing, according to some embodiments. Forinstance, in one embodiment, some or all of the first padding bits areadded to the information bits by a padding system of the MAC unit 18, 28(FIG. 1). In one embodiment, some or all of the first padding bits areadded to the information bits after encoder parsing. The block 904 isimplemented at least partly by the padding system 600 (FIG. 13), in oneembodiment, or by another suitable padding system. For example, block904 is implemented by the padding unit 604, in one embodiment.

At block 908, the information bits and the zero or more first paddingbits are encoded by one or more convolutional encoders. Block 908includes parsing the information bit and the zero or more first paddingbits to the one or more FEC encoders. In one embodiment, block 908 isimplemented by the encoder parser 208 and one or more of the FECencoders 212 (FIG. 3).

At block 912, second padding bits are added to the encoded informationand first padding bits. Block 912 is implemented at least partly by thepadding system 600 (FIG. 13), in one embodiment, or by another suitablepadding system. For example, block 912 is implemented by the paddingunit 612, in one embodiment.

At block 916, the encoded information bits and first padding bits andthe second padding bits are modulated. Block 916 is implemented by oneor more of the constellation mappers 224 (FIG. 3), according to anembodiment.

At block 920, one or more OFDM symbols are formed. In one embodiment,block 920 is implemented at least partially by one or more of the IDFTunits 240 and one or more of the GI and window units 244 (FIG. 3).

FIG. 21 is a flow diagram of another example method 950 for generating aPHY data unit for transmission via a communication channel, according toanother embodiment. The PHY unit 20, 29 (FIG. 1) is configured toimplement the method 950 at least partially, in one embodiment.Similarly, the PHY unit 200 (FIG. 3) is configured to implement themethod 950 at least partially, in another embodiment. In otherembodiments, another suitable PHY unit is configured to implement themethod 950 at last partially.

At block 954, a first set of MCS's and a second set of MCS's areprovided, where the first set and the second set both correspond to agiven number of spatial streams and a given number of encoders, andwhere the first set corresponds to a first channel bandwidth and thesecond set corresponds to a second channel bandwidth. The first set isdifferent than the second set.

In one embodiment, the first set of MCS's and the second set of MCS'sare provided in separate MCS tables corresponding to different channelbandwidths. In another embodiment, the first set of MCS's and the secondset of MCS's are provided in a single MCS table, and an index to thesingle MCS table is interpreted differently depending on the channelbandwidth to be used to transmit the PHY data unit. For example, theindex to the single MCS table is interpreted to select only from thefirst set of MCS's when the first channel bandwidth is to be used,whereas the index to the single MCS table is interpreted to select onlyfrom the second set of MCS's when the second channel bandwidth is to beused.

In one embodiment, the first set of MCS's excludes MCS's that willresult in excessive numbers of padding bits and/or dummy OFDM symbolswhen the first channel bandwidth is to be used, and the second set ofMCS's excludes MCS's that will result in excessive numbers of paddingbits and/or dummy OFDM symbols when the second channel bandwidth is tobe used. In another embodiment, the first set of MCS's excludes MCS'sthat result in one or more padding bit-related constraints failing to bemet when the first channel bandwidth is to be used, and the second setof MCS's excludes MCS's that do not satisfy the one or more paddingbit-related constraints when the second channel bandwidth is to be used.

At block 958, an MCS is selected from the first set when the PHY dataunit is to be transmitted in a channel having the first channelbandwidth. At block 962, an MCS is selected from the second set when thePHY data unit is to be transmitted in a channel having the secondchannel bandwidth.

At block 966, a payload is encoded according to the selected MCS. Block966 includes parsing the payload to one or more FEC encoders. In oneembodiment, block 966 is implemented by the encoder parser 208 and oneor more of the FEC encoders 212 (FIG. 3).

At block 970, the encoded payload is modulated. Block 970 is implementedby one or more of the constellation mappers 224 (FIG. 3), according toan embodiment.

At block 974, one or more OFDM symbols are formed. In one embodiment,block 974 is implemented at least partially by one or more of the IDFTunits 240 and one or more of the GI and window units 244 (FIG. 3).

FIG. 22 is a flow diagram of another example method 1000 for generatinga PHY data unit for transmission via a communication channel, accordingto another embodiment. The PHY unit 20, 29 (FIG. 1) is configured toimplement the method 1000 at least partially, in one embodiment.Similarly, the PHY unit 200 (FIG. 3) is configured to implement themethod 950 at least partially, in another embodiment. In otherembodiments, another suitable PHY unit is configured to implement themethod 950 at last partially.

At block 1004, a first set of MCS's that correspond to a first channelbandwidth is provided. At block 1008, a second set of MCS's thatcorrespond to a second channel bandwidth is provided, wherein providingthe second set of MCS's includes excluding MCS's from the first set ofMCS's that do not satisfy a constraint related to padding. In oneembodiment, the first set of MCS's and the second set of MCS's eachexclude MCS's that do not satisfy the constraint, but one or more MCS'sin the first set satisfy the constraint with respect to the firstchannel bandwidth, but these one or more MCS's do not satisfy theconstraint with respect to the second channel bandwidth. In oneembodiment, the constraint corresponds to Equ. 27 and/or the constraintis that

$\frac{N_{DBPS}}{N_{ES}}\mspace{14mu}{and}\mspace{14mu}\frac{N_{CBPS}}{N_{ES}}$are integers. In another embodiment, the constraint is that bothN_(DBPS) and N_(CBPS) are integers.

In one embodiment, the first set of MCS's and the second set of MCS'sare provided in separate MCS tables corresponding to the differentchannel bandwidths. In another embodiment, the first set of MCS's andthe second set of MCS's are provided in a single MCS table, and an indexto the single MCS table is interpreted differently depending on thechannel bandwidth to be used to transmit the PHY data unit. For example,the index to the single MCS table is interpreted to select only from thefirst set of MCS's when the first channel bandwidth is to be used,whereas the index to the single MCS table is interpreted to select onlyfrom the second set of MCS's when the second channel bandwidth is to beused.

In one embodiment, the first set of MCS's excludes MCS's that willresult in excessive numbers of padding bits and/or dummy OFDM symbolswhen the first channel bandwidth is to be used, and the second set ofMCS's excludes MCS's that will result in excessive numbers of paddingbits and/or dummy OFDM symbols when the second channel bandwidth is tobe used. In another embodiment, the first set of MCS's excludes MCS'sthat result in one or more padding bit-related constraints failing to bemet when the first channel bandwidth is to be used, and the second setof MCS's excludes MCS's that do not satisfy the one or more paddingbit-related constraints when the second channel bandwidth is to be used.

At block 1012, an MCS is selected from the first set when the PHY dataunit is to be transmitted in a channel having the first channelbandwidth. At block 1016, an MCS is selected from the second set whenthe PHY data unit is to be transmitted in a channel having the secondchannel bandwidth.

At block 1018, padding bits are added to information bits to generatepayload information.

At block 1020, the payload information is encoded according to theselected MCS. Block 1020 includes parsing the payload to one or more FECencoders. In one embodiment, block 1020 is implemented by the encoderparser 208 and one or more of the FEC encoders 212 (FIG. 3). In someembodiments, padding bits are added after encoding.

At block 1024, the encoded payload is modulated. Block 1024 isimplemented by one or more of the constellation mappers 224 (FIG. 3),according to an embodiment.

At block 1028, one or more OFDM symbols are formed. In one embodiment,block 1028 is implemented at least partially by one or more of the IDFTunits 240 and one or more of the GI and window units 244 (FIG. 3).

FIG. 23 is a flow diagram of another example method 1050 for generatinga PHY data unit for transmission via a communication channel, accordingto another embodiment. The PHY unit 20, 29 (FIG. 1) is configured toimplement the method 1050 at least partially, in one embodiment.Similarly, the PHY unit 200 (FIG. 3) is configured to implement themethod 1050 at least partially, in another embodiment. In otherembodiments, another suitable PHY unit is configured to implement themethod 1050 at last partially.

At block 1054, a modulation scheme is selected from a set of possiblemodulation schemed that can be utilized.

At block 1058, payload information is encoded. Block 1058 includesparsing the payload information to one or more FEC encoders. In oneembodiment, block 1058 is implemented by the encoder parser 208 and oneor more of the FEC encoders 212 (FIG. 3).

At block 1062, the interleaving parameter N_(COL) is selected from aplurality of different values. N_(COL) is selected using or based on theselected modulation scheme. For example, for a given channel bandwidth,N_(COL) may be different for different constellation sizes, according toan embodiment.

At block 1066, the encoded payload information is interleaved, whichincludes entering encoded data into N_(ROW) and reading the encoded dataout in N_(COL) columns. Block 1066 is implemented by one or more of theinterleavers 220 (FIG. 3), according to an embodiment.

At block 1070, the encoded and interleaved payload information ismodulated according to the selected modulation scheme. Block 1070 isimplemented by one or more of the constellation mappers 224 (FIG. 3),according to an embodiment.

At block 1074, one or more OFDM symbols are formed. In one embodiment,block 1024 is implemented at least partially by one or more of the IDFTunits 240 and one or more of the GI and window units 244 (FIG. 3).

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for generating a physical layer (PHY)data unit for transmission via a communication channel, the methodcomprising: selecting, at a communication device, a modulation codingscheme (MCS) i) from a first set of MCSs when the PHY data unit is to betransmitted using a channel having a first channel bandwidth, and ii)from a second set of MCSs when the PHY data unit is to be transmittedusing a channel having a second channel bandwidth, wherein the first setof MCSs corresponds to i) a number of spatial streams, and ii) the firstchannel bandwidth, the second set of MCSs corresponds to i) the numberof spatial streams, and ii) the second channel bandwidth, the first setof MCSs is different than the second set of MCSs, and the second set ofMCSs excludes one or more MCSs in the first set of MCSs that will resultin a padding-related constraint not being met when the second channelbandwidth is to be used; encoding, at the communication device,information bits using one or more encoders and according to theselected MCS; parsing, at the communication device, the encodedinformation bits into the number of spatial streams; modulating, at thecommunication device, the encoded information bits according to theselected MCS; and generating, at the communication device, a pluralityof Orthogonal Frequency Division Multiplexing (OFDM) symbols based onthe modulated encoded information bits.
 2. The method of claim 1,wherein: the number of spatial streams is three; the second channelbandwidth is 80 MHz; the first set of MCSs includes an MCS correspondingto 64-QAM modulation and rate 3/4 encoding; and the second set of MCSsexcludes the MCS corresponding to 64-QAM modulation and rate 3/4encoding.
 3. The method of claim 1, wherein the first set of MCSsexcludes one or more MCSs in the second set of MCSs that will result inthe padding-related constraint not being met when the first channelbandwidth is to be used.
 4. The method of claim 3, wherein: the numberof spatial streams is three; the first channel bandwidth is 160 MHz; thesecond channel bandwidth is 80 MHz; the first set of MCSs includes anMCS corresponding to 64-QAM modulation and rate 3/4 encoding; the secondset of MCSs excludes the MCS corresponding to 64-QAM modulation and rate3/4 encoding; the second set of MCSs includes an MCS corresponding to256-QAM modulation and rate 5/6 encoding; and the first set of MCSsexcludes the MCS corresponding to 256-QAM modulation and rate 5/6encoding.
 5. The method of claim 1, wherein selecting the MCS comprises:selecting the MCS i) from a first MCS table corresponding to i) thenumber of spatial streams, and ii) the first channel bandwidth when thePHY data unit is to be transmitted using a channel having the firstchannel bandwidth and using the number of spatial streams; and selectingthe MCS i) from a second MCS table corresponding to i) the number ofspatial streams, and ii) the second channel bandwidth when the PHY dataunit is to be transmitted using a channel having the second channelbandwidth and using the number of spatial streams; wherein the secondtable excludes the one or more MCSs in the first set of MCSs that willresult in the padding-related constraint not being met when the secondchannel bandwidth is to be used.
 6. The method of claim 1, whereinselecting the MCS comprises: selecting the MCS from an MCS table; andinterpreting the MCS table differently when the PHY data unit is to betransmitted using the first channel bandwidth as compared to when thePHY data unit is to be transmitted using the second channel bandwidth.7. The method of claim 1, further comprising: adding, at a media accesscontrol (MAC) unit of the communication device, padding delimiters to anend of a MAC data unit to be included in the PHY data unit; and adding,at a PHY unit of the communication device, PHY padding to the PHY dataunit.
 8. The method of claim 1, wherein: the second channel bandwidth is80 MHz; and when the second channel bandwidth is to be used, generatingthe plurality of OFDM symbols comprises generating OFDM symbols having256 subcarriers, with data tones and pilot tones i) at subcarrierindices −122 to −2 and ii) at subcarrier indices 2 to
 122. 9. The methodof claim 8, wherein: when the second channel bandwidth is to be used,generating the plurality of OFDM symbols comprises generating OFDMsymbols with guard tones only at subcarrier indices i) −128 to −123 andii)+123 to +127, and DC tones only at subcarrier indices −1 to +1. 10.The method of claim 8, wherein: when the second channel bandwidth is tobe used, generating the plurality of OFDM symbols comprises generatingOFDM symbols with pilot tones at subcarrier indices −103, −75, −39, −11,11, 39, 75, and
 103. 11. An apparatus, comprising: a network interfacedevice including: a memory to store indicators of a first set ofmodulation coding schemes (MCSs) and a second set of MCSs, wherein thefirst set of MCSs corresponds to i) a number of spatial streams, and ii)the first channel bandwidth, the second set of MCSs corresponds to i)the number of spatial streams, and ii) the second channel bandwidth, thefirst set of MCSs is different than the second set of MCSs, and thesecond set of MCSs excludes one or more MCSs in the first set of MCSsthat will result in a padding-related constraint not being met when thesecond channel bandwidth is to be used; wherein the network interfacedevice is configured to select an MCS i) from the first set of MCSs whena physical layer (PHY) data unit is to be transmitted using a channelhaving a first channel bandwidth, and ii) from the second set of MCSswhen the PHY data unit is to be transmitted using a channel having asecond channel bandwidth; wherein the network interface device furtherincludes: one or more encoders configured to encode information bitsaccording to the selected MCS, a parser configured to parse the encodedinformation bits into the number of spatial streams, and a modulatorconfigured to modulate the encoded information bits according to theselected MCS; and wherein the network interface device is furtherconfigured to generate a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols based on the modulated encoded informationbits.
 12. The apparatus of claim 11, wherein: the number of spatialstreams is three; the second channel bandwidth is 80 MHz; the first setof MCSs includes an MCS corresponding to 64-QAM modulation and rate 3/4encoding; and the second set of MCSs excludes the MCS corresponding to64-QAM modulation and rate 3/4 encoding.
 13. The apparatus of claim 11,wherein the first set of MCSs excludes one or more MCSs in the secondset of MCSs that will result in the padding-related constraint not beingmet when the first channel bandwidth is to be used.
 14. The apparatus ofclaim 13, wherein: the number of spatial streams is three; the firstchannel bandwidth is 160 MHz; the second channel bandwidth is 80 MHz;the first set of MCSs includes an MCS corresponding to 64-QAM modulationand rate 3/4 encoding; the second set of MCSs excludes the MCScorresponding to 64-QAM modulation and rate 3/4 encoding. the second setof MCSs includes an MCS corresponding to 256-QAM modulation and rate 5/6encoding. the first set of MCSs excludes the MCS corresponding to256-QAM modulation and rate 5/6 encoding.
 15. The apparatus of claim 11,wherein: the memory is configured to store: a first MCS tablecorresponding to i) the number of spatial streams, and ii) the firstchannel bandwidth, the first MCS table storing indicators of the firstset of MCSs, and a second MCS table corresponding to i) the number ofspatial streams, and ii) the second channel bandwidth, the second MCStable storing indicators of the second set of MCSs; the networkinterface device is configured to: select the MCS from the first MCStable when the PHY data unit is to be transmitted using a channel havingthe first channel bandwidth and using the number of spatial streams, andselect the MCS from the second MCS table when the PHY data unit is to betransmitted using a channel having the second channel bandwidth andusing the number of spatial streams; the second MCS table excludes oneor more indicators of the one or more MCSs in the first set of MCSs thatwill result in the padding-related constraint not being met when thesecond channel bandwidth is to be used.
 16. The apparatus of claim 11,wherein: the memory is configured to store an MCS table storingindicators of MCSs; and the network interface device is configured to:selecting the MCS from the MCS table, and interpret the MCS tabledifferently when the PHY data unit is to be transmitted using the firstchannel bandwidth as compared to when the PHY data unit is to betransmitted using the second channel bandwidth.
 17. The apparatus ofclaim 11, wherein the network interface device includes: a media accesscontrol (MAC) unit configured to add padding delimiters to an end of aMAC data unit to be included in the PHY data unit; and a PHY unitconfigured to add PHY padding to the PHY data unit.
 18. The apparatus ofclaim 11, wherein: the second channel bandwidth is 80 MHz; and thenetwork interface device is configured to, when the second channelbandwidth is to be used, generate the plurality of OFDM symbols to have256 subcarriers, with data tones and pilot tones i) at subcarrierindices −122 to −2 and ii) at subcarrier indices 2 to
 122. 19. Theapparatus of claim 18, wherein the network interface device isconfigured to: when the second channel bandwidth is to be used, generatethe OFDM symbols with guard tones only at subcarrier indices i) −128 to−123 and ii)+123 to +127, and DC tones only at subcarrier indices −1 to+1.
 20. The apparatus of claim 18, wherein the network interface deviceis configured to: when the second channel bandwidth is to be used,generate the OFDM symbols with pilot tones at subcarrier indices −103,−75, −39, −11, 11, 39, 75, and 103.